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Author Topic: Results of six-month 'window test' on inkjet coatings  (Read 27255 times)

shadowblade

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Results of six-month 'window test' on inkjet coatings
« on: March 08, 2014, 03:10:43 PM »

I've been doing a rough 'window test' on a number of different papers over the past six months to estimate the long-term stability of their inkjet coatings, owing to the very limited information regarding this out there (as opposed to information on lightfastness).

Basically, I mounted a number of pieces of paper onto the inside of a north-facing window and let them bake over the Australian spring and summer (using Blu-Tack, so that the paper wasn't actually touching the glass) and checked on them from time to time to see how they held up. Humidity and temperature fluctuated as they would in an un-airconditioned home environment (I was away most of the time, so heating/air con were left off for the most part). Not all that rigorous, I know, but good enough to get an idea of what to expect.

The papers tested were:

Fuji Crystal Archive (resin-coated chromogenic)
Moab Slickrock Metallic Pearl (resin-coated)
Hahnemuhle Photo Glossy (resin-coated)
Hahnemuhle Photo Rag Baryta (baryta)
Ilford Gold Fibre Silk (baryta)
Hahnemuhle Photo Rag Pearl (cotton rag)
Hahnemuhle Photo Rag (cotton rag)
Canson Etching Edition (cotton rag)

All of them except the Fuji Crystal Archive included one unsprayed piece and one piece sprayed with Hahnemuhle Protective Spray.

The results?

- After two months, the Fuji Crystal Archive had curled up so badly that it fell off the Blu-Tack; trying to uncurl it merely resulted in the polythene layer cracking across the entire width of the sheet.

- After three months, the receptive layer on the unsprayed RC inkjet papers had both disintegrated to the point that merely touching it caused the layer to come off onto the finger as a powder. The sprayed RC papers held up better, but were still showing some signs of flaking (i.e. the inkjet layer was coming off the resin layer, but was being held together at the front by the spray). After five months, the sprayed RC papers were also flaking badly, with large flakes falling when touching the paper.

- After six months, the baryta papers were also curling, delaminating, flaking and cracking. Again, the sprayed sheets held up better than the unsprayed sheets. The Hahnemuhle Photo Rag Baryta also held up much better than the IGFS. I couldn't tell whether it was the inkjet layer coming off the baryta layer or the baryta layer coming off the paper base. I suspect it may have been the latter, given that the paper base would have been shrinking and expanding with changes in humidity while bound to the rigid, inflexible baryta layer.

- The cotton rag papers held up much better than the others. Not surprising, really, given that these essentially consist of a thin, relatively-flexible coating of polyvinyl alcohol and silica directly bonded to a thicker and less-flexible paper base, with no in-between layer. At six months, I didn't notice any peeling or cracking in either the sprayed or unsprayed samples.

Obviously this is a quick test rather than a detailed scientific study - I'm still not certain about the long-term durability of any of these coatings, but at least know which types are the better ones.

Does anyone know what sort of surface sizing Hahnemuhle and Canson use in their papers, prior to inkjet coating? If they size their papers with polyvinyl alcohol, it would make make sense for the coating-paper bond to be even stronger - after all, the coating and the paper's external size would be the same material. Although it could just be that a thin, flexible PVOH layer can conform to an expanding and contracting paper base much better than a rigid baryta or resin layer can, and that PVOH just doesn't stick all that well to plastic...
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Geraldo Garcia

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #1 on: March 08, 2014, 05:36:18 PM »

Nice test!
Thanks for posting.
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Wayne Fox

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #2 on: March 08, 2014, 06:22:20 PM »

Fading from of UV light is sort of accumulative, exposing to very bright UV light does translate to a somewhat effective age acceleration test.  Heat on the other hand is not accumulative.  Placing the prints in the manner you describe seems a very abnormal condition with temperatures much greater over sustained periods of time, and while certainly informative in some circumstances, I don't think you can draw any real conclusions, unless you expect the prints to be in a similar environment.  Sitting right against a sunlit window doesn't sound like the type of thermal characteristics one would expect a print to be in ... maybe a sign or poster, but not a quality photograph created for exhibit.  As an example, RC prints that are decades old do not exhibit the kinds of issues you have describe unless they have been subjected to unusual storage conditions, so how does your test correlate?  I have had a fuji flex print sitting in the east facing window of my store for about a year, and it is showing signs of fading, but no physical issues at all.

Unfortunately I don't believe there is a way to do an "accelerated deterioration test", but then again the conditions of any environment go beyond just light and heat, and are wildly variable.

shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #3 on: March 08, 2014, 08:04:08 PM »

Fading from of UV light is sort of accumulative, exposing to very bright UV light does translate to a somewhat effective age acceleration test.  Heat on the other hand is not accumulative.  Placing the prints in the manner you describe seems a very abnormal condition with temperatures much greater over sustained periods of time, and while certainly informative in some circumstances, I don't think you can draw any real conclusions, unless you expect the prints to be in a similar environment.  Sitting right against a sunlit window doesn't sound like the type of thermal characteristics one would expect a print to be in ... maybe a sign or poster, but not a quality photograph created for exhibit.  As an example, RC prints that are decades old do not exhibit the kinds of issues you have describe unless they have been subjected to unusual storage conditions, so how does your test correlate?  I have had a fuji flex print sitting in the east facing window of my store for about a year, and it is showing signs of fading, but no physical issues at all.

Unfortunately I don't believe there is a way to do an "accelerated deterioration test", but then again the conditions of any environment go beyond just light and heat, and are wildly variable.

This wasn't a thermal test. It was a test of how a print would handle in a non-museum home or commercial environment after exposure to UV light - specifically, due to embrittlement of the inkjet coating or other layers, or due to failure of bonds between the layers. After all, everyone knows that inkjet papers start off flexible, but we don't really know whether they'll stay that way with UV exposure. It's like gesso or paint coming off an old oil-on-canvas painting as it stretches and sags on its frame during changes in humidity. For this reason, I also flexed the paper in each direction every month to see if anything flaked off.

Temperatures experienced by the paper ranged from 8-40 degrees Celcius - normal conditions around here. Relative humidity ranged from 20-95%. With regards to pollutants, it was indoors, in the middle of a big city. So, no unusual environmental stresses there - just what you'd expect in a typical home environment, but with accelerated UV exposure.
« Last Edit: March 08, 2014, 08:21:51 PM by shadowblade »
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Farmer

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #4 on: March 08, 2014, 08:50:00 PM »

As Wayne points out, you didn't just "accelerate" UV exposure, you also subjected it to direct sunlight millimetres from glass.  That would have significantly impacted the heat levels on the media compared to a normal presentation hanging on a wall inside a home.

This is nothing like the environment in which most prints will exist, being either mounted to a board or behind glass or both, and sitting on a wall out of direct sunlight most of the time and certainly well away from an external window.

You also had the media without an ink load, which may also impact (I don't know, but it's a pretty key difference so it shouldn't be ignored).

As an Aussie, I can attest to the fact that putting your face against a North facing window in summer when it's hot is extremely uncomfortable - I dare say you could burn yourself (not just sunburn) with any prolonged exposure.  We also have higher UV levels here than most other parts of the world, so the total impact on the media is quite extreme an unrealistic.
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Phil Brown

shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #5 on: March 09, 2014, 06:52:53 AM »

As Wayne points out, you didn't just "accelerate" UV exposure, you also subjected it to direct sunlight millimetres from glass.  That would have significantly impacted the heat levels on the media compared to a normal presentation hanging on a wall inside a home.

Surprisingly not. In the afternoon of the hottest day of the summer (44 degrees outdoor shade temperature), with no cloud cover and light streaming in through the window, the papers all measured between 37 and 39 degrees Celcius. This is because the near-white papers reflected most of the incoming solar radiation. In contrast, the black silicone sealant around the window measured at 88 degrees Celcius at the same time.

If I had printed the sheets, no doubt the temperature would have been a lot higher.

In any case, short periods of high temperatures are normal for photos and paintings displayed in home environments if they're displayed in any location that receives direct sunlight. Usually, a photo's location is chosen for aesthetic and interior design reasons, not print preservation concerns, and many of these locations receive direct sunlight at some time of the day at some point in the year. It's only museums, galleries and collections that deliberately locate works away from sunlight. And it doesn't take a lot of direct sunlight from an cloudless sky on a hot day to heat a printed image - often with dark inks, and usually stored inside an enclosed frame that essentially acts as a greenhouse and traps heat - to 50-60 degrees or hotter.

Quote
This is nothing like the environment in which most prints will exist, being either mounted to a board or behind glass or both, and sitting on a wall out of direct sunlight most of the time and certainly well away from an external window.

Blasting a print with 50klux xenon lamps for 12 or 24 hours a day also isn't anything like the environment in which most prints would be displayed. The point of accelerated testing isn't to simulate the environment the prints are going to be kept in - the only way to do that would be to hang sets of prints in various places for 50/100/200 years and see what happens. It's to simulate what will happen to paper when it's subjected to real-world fluctuations in humidity and temperature, as well as movement/flexion, after its been blasted by UV radiation to the equivalent of 50/100/200 years in normal display. In other words, what will happen to the paper when its been on display for a few decades and you then try to change the mat/frame, unframe it and send it by courier, move it to a new place or otherwise handle it in any other way, or what will happen to even a framed, unmoved print given a bit more time and normal humidity-related paper fluctuations.

Quote
You also had the media without an ink load, which may also impact (I don't know, but it's a pretty key difference so it shouldn't be ignored).

I was debating whether to run the test with or without ink. In the end, I went without ink because I didn't want temperature to become an issue (dark surfaces can become 30-40 degrees hotter than light-coloured surfaces in the sun) and because every print will have areas of light or no coverage (e.g. the print borders, at least a narrow strip of which won't be covered by the mat). If these light/no coverage areas fail, then the print as a whole has failed, whether the heavily-inked parts are OK or not.

Quote
As an Aussie, I can attest to the fact that putting your face against a North facing window in summer when it's hot is extremely uncomfortable - I dare say you could burn yourself (not just sunburn) with any prolonged exposure.  We also have higher UV levels here than most other parts of the world, so the total impact on the media is quite extreme an unrealistic.

UV exposure here is definitely higher, but that's just like deciding to use 50klux lamps for permanence testing instead of 20klux lamps. Both are valid. Naturally, you can't directly compare results from a 50klux test against a 20klux test (due to the possibility of reciprocity failure), but, when you're testing multiple samples against each other, in the same environment, you can safely say whether one particular paper performs better or worse than another. In other words, the results are more qualitative rather than quantitative, but you can say the same for most accelerated testing regimes, since speeding up the UV illumination doesn't speed up gas fading, dark fading, humidity and biological effects which also deteriorate the print.
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Ernst Dinkla

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #6 on: March 09, 2014, 09:10:15 AM »


Obviously this is a quick test rather than a detailed scientific study - I'm still not certain about the long-term durability of any of these coatings, but at least know which types are the better ones.

Does anyone know what sort of surface sizing Hahnemuhle and Canson use in their papers, prior to inkjet coating? If they size their papers with polyvinyl alcohol, it would make make sense for the coating-paper bond to be even stronger - after all, the coating and the paper's external size would be the same material. Although it could just be that a thin, flexible PVOH layer can conform to an expanding and contracting paper base much better than a rigid baryta or resin layer can, and that PVOH just doesn't stick all that well to plastic...

Not scientific but still interesting.

I think that the compatibility of the sizing and the coating medium could have an influence (does not even have to be the same "glue") but you also should count the roughness of the paper base at the bond level. Not only does a rougher surface increase the bond's surface but its geometry also dampens the expansion and shrinking forces over the total surface. A smooth paper based inkjet paper has a more uniform layer structure, say planes on top of one another that have more problems with heat/humidity expansion differences. I feared that the polyethylene barriers in RC paper would create an issue on the coating bond anyway, PE is quite inert and needs Corona treatment to create a better bond for inks and glues. Even then a weak bond. If the coating is not much more than gelatine or PVA like in analogue photo papers then the flexibility of coating will cope as long as that flexibility is kept, it will be harder when minerals are introduced in the coating like it is done in the inkjet coatings we use today. That the fiber/baryta papers are not free of mechanical wear is interesting too. The sizing compatibility should not be that different to that of the cotton papers.
Your paper summary is a bit confusing. Barytes are used in papers without them mentioned in the product name and the Photo Rag Baryta is a cotton paper. There might be a relation between the roughness of the paper base (most cotton but also some alpha cellulose qualities are rough at the base) and the compensation of expansion etc. For smoother inkjet paper surfaces there is a distinction between creating them on smooth paper bases or creating a smooth surface on rougher paper bases, say only satinised after applying the inkjet coating and not twice in the inkjet paper creation. A rougher backside can give an indication though it is possible to make a paper base with one side (hot press) satinised while the other side keeps a rougher surface.

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Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
January 2014, 600+ inkjet media white spectral plots
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MHMG

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #7 on: March 09, 2014, 10:34:26 AM »

Another interesting study would be to rerun your test only behind a piece of museum glass. It would eliminate 99% of the worrisome UV content and allow you to study the temperature/moisture issues without the confounding issue of UV exposure. My hypothesis is that you will induce very nearly the same results even without the UV component present. The key antagonist in this test is the severe heat/desiccation cycling caused by the lack of moisture control at the sample plane. All print media are very hygroscopic in nature. 40% RH at normal room temperature represents the ideal internal moisture content for essentially all of the media you tested.  Expansion/contractions caused by moisture changes in these hygroscopic materials are typically 10 times greater than that caused by temperature change, and those severe dimensional mismatches between the layers lead to severe internal mechanical stresses. With traditional photographic gelatin (i.e the Fuji Crystal archive image bearing layer) for example, the contracting gelatin layers can place a huge tensile stress on a rigid support layer (glass or polyester, for example) of over 6000 psi. Dry gelatin coatings are stronger than epoxy coatings!  When the sunlight cycle is over, the nighttime cycle starts to cool and rehydrate the coatings and base, but some hysteresis in the dimensional properties still remains, i.e., it doesn't return to precisely the same dimensional configuration where it initially started. Then the next sunlight cycle induces the stress cycle all over again. Micro cracks start to form which ultimately propagate into larger cracks. It take much less energy to propagate an existing crack than to form it initially.  Adhesion between coatings and base gets damaged for the same reasons.

When the sun bakes these materials to 40C+, the moisture content will drop to a level well below that encountered in normal daily indoor environments (i.e. equivalent of less than 5% RH indoor prolonged humidity level). That said, this "accelerated" test does bear some rough chemical/physical relationship to what can/will happen to coated media in long term keeping conditions where strong seasonal cycles are present (albeit taking these materials well beyond their rational mechanical limits, kind of like when you bend a print to the point of creasing it). So, in very rough terms your six month/180 day test is something like 180 years of severe seasonal cycling, i.e, keeping a photograph with no moisture barrier protection in a home that has no HVAC system to regulate humidity, just supply indoor heat during the winter but no cooling/dehumidification indoors during the summer. Now you can understand why museum experts attempt to control indoor environments more tightly in order to better preserve important artistic/historic works.  Homeowners with fine art/historic collections in their possession should consider some HVAC upgrades as well. And don't put your fine art, whether it be photograph, painting, or uncoated paper in a window :)

cheers,
Mark
http://www.aardenburg-imaging.com
« Last Edit: March 09, 2014, 11:03:52 AM by MHMG »
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AFairley

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #8 on: March 09, 2014, 11:57:35 AM »

Interesting test,and thanks for carrying it out.  However, I suspect that putting the prints that close to the glass created a micro-environment between the print and the glass that was much much hotter than the ambient temperature. You're creating a heat trap since there's no possibility of air circulation carrying away the hot air on the surface of the print.  I think a better test would be to have the prints a foot or two away from the window.  But very interesting results nonetheless.
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Czornyj

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #9 on: March 09, 2014, 12:51:15 PM »

My hypothesis is that you will induce very nearly the same results even without the UV component present. The key antagonist in this test is the severe heat/desiccation cycling caused by the lack of moisture control at the sample plane. All print media are very hygroscopic in nature. 40% RH at normal room temperature represents the ideal internal moisture content for essentially all of the media you tested.

Mark, I totally agree with your hypothesis. I'm regularly ironing my prints and my observations were 99% consistent to shadowblade test results - PE type papers crack very easily, baryta papers with anti-curl layers can also be destroyed, Hahnemuehle baryta papers and matte calendared are most heat-resistant, while matte heavily textured papers can also be problematic.

TylerB

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #10 on: March 09, 2014, 01:57:30 PM »

I'm curious if you observe, with the matte rag papers, Hahnemuhle Photo Rag and Canson Etching Edition, any tendency for the clay-like receptor coating to become more powdery, flaky, or lose it's physical integrity or in any way. Might require some slight abuse to induce anything noticeable?
I found the test info useful, it all helps.
Thanks,
Tyler
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steveclv

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #11 on: March 09, 2014, 02:29:40 PM »

I think the test would have been more educational had the same image been printed on each paper and then the images all mounted on a board that was 12' away from the window getting full sunshine.

The intense heat that is created through the glass was so artificial an environment that I believe that it corrupted the results. UV is what we are interested in, not 50+C temps.

Just my AUS$0.02 :)
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shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #12 on: March 09, 2014, 02:38:19 PM »

I think the test would have been more educational had the same image been printed on each paper and then the images all mounted on a board that was 12' away from the window getting full sunshine.

The intense heat that is created through the glass was so artificial an environment that I believe that it corrupted the results. UV is what we are interested in, not 50+C temps.

Just my AUS$0.02 :)

Interesting test,and thanks for carrying it out.  However, I suspect that putting the prints that close to the glass created a micro-environment between the print and the glass that was much much hotter than the ambient temperature. You're creating a heat trap since there's no possibility of air circulation carrying away the hot air on the surface of the print.  I think a better test would be to have the prints a foot or two away from the window.  But very interesting results nonetheless.

The temperature of the paper, as measured even on the hottest afternoon on the year, never exceeded 37-39 degrees and the circulation around paper Blu-Tacked to the window is much greater than any air circulation you'd have around a framed and matted print.

Besides, *any* print that is put in a location that receives direct sunlight will exceed 50 degrees at some point. Framing and matting a print behind glass is the real heat trap - it functions just like a greenhouse. Solar radiation hits the print and gets absorbed by the darker inks (much more so than white paper - note the reading of 88 degrees on the black surface next to the white paper when it was measuring 39 degrees). The hot paper surface then heats up the air within the frame, which is trapped behind the glass and keeps the print warm for much longer than the period of solar irradiation.
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shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #13 on: March 09, 2014, 04:07:03 PM »

Another interesting study would be to rerun your test only behind a piece of museum glass. It would eliminate 99% of the worrisome UV content and allow you to study the temperature/moisture issues without the confounding issue of UV exposure. My hypothesis is that you will induce very nearly the same results even without the UV component present. The key antagonist in this test is the severe heat/desiccation cycling caused by the lack of moisture control at the sample plane. All print media are very hygroscopic in nature. 40% RH at normal room temperature represents the ideal internal moisture content for essentially all of the media you tested.  Expansion/contractions caused by moisture changes in these hygroscopic materials are typically 10 times greater than that caused by temperature change, and those severe dimensional mismatches between the layers lead to severe internal mechanical stresses. With traditional photographic gelatin (i.e the Fuji Crystal archive image bearing layer) for example, the contracting gelatin layers can place a huge tensile stress on a rigid support layer (glass or polyester, for example) of over 6000 psi. Dry gelatin coatings are stronger than epoxy coatings!  When the sunlight cycle is over, the nighttime cycle starts to cool and rehydrate the coatings and base, but some hysteresis in the dimensional properties still remains, i.e., it doesn't return to precisely the same dimensional configuration where it initially started. Then the next sunlight cycle induces the stress cycle all over again. Micro cracks start to form which ultimately propagate into larger cracks. It take much less energy to propagate an existing crack than to form it initially.  Adhesion between coatings and base gets damaged for the same reasons.

I'm not so sure about that. Certainly, the dessication/rehydration cycle is the primary driver of dimensional change in papers. But the primary driver of stress at the interface layer isn't dimensional change per se - rather, it is a product of dimensional change in the paper as well as resistance to dimensional change and flexion in the coating layer. Unexposed to UV light, a polyvinyl alcohol film (even embedded with silica particles) is supple and flexible - this is why we are able to bend and stretch inkjet canvas. But, with prolonged UV exposure, I suspect the layer becomes stiffer and more brittle - it is this resistance to the paper's dimensional change that causes stress to build up along the interface, resulting in failure of the bond, cracking and delamination.

Quote
When the sun bakes these materials to 40C+, the moisture content will drop to a level well below that encountered in normal daily indoor environments (i.e. equivalent of less than 5% RH indoor prolonged humidity level). That said, this "accelerated" test does bear some rough chemical/physical relationship to what can/will happen to coated media in long term keeping conditions where strong seasonal cycles are present (albeit taking these materials well beyond their rational mechanical limits, kind of like when you bend a print to the point of creasing it). So, in very rough terms your six month/180 day test is something like 180 years of severe seasonal cycling, i.e, keeping a photograph with no moisture barrier protection in a home that has no HVAC system to regulate humidity, just supply indoor heat during the winter but no cooling/dehumidification indoors during the summer. Now you can understand why museum experts attempt to control indoor environments more tightly in order to better preserve important artistic/historic works.  Homeowners with fine art/historic collections in their possession should consider some HVAC upgrades as well. And don't put your fine art, whether it be photograph, painting, or uncoated paper in a window :)

cheers,
Mark
http://www.aardenburg-imaging.com

I suspect the same thing would happen to a framed paper exposed to direct sunlight. After all, there's much more air circulation around an unframed piece of paper than there is in a framed image.
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Wayne Fox

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #14 on: March 09, 2014, 04:21:48 PM »

The temperature of the paper, as measured even on the hottest afternoon on the year, never exceeded 37-39 degrees and the circulation around paper Blu-Tacked to the window is much greater than any air circulation you'd have around a framed and matted print.

Besides, *any* print that is put in a location that receives direct sunlight will exceed 50 degrees at some point. Framing and matting a print behind glass is the real heat trap - it functions just like a greenhouse. Solar radiation hits the print and gets absorbed by the darker inks (much more so than white paper - note the reading of 88 degrees on the black surface next to the white paper when it was measuring 39 degrees). The hot paper surface then heats up the air within the frame, which is trapped behind the glass and keeps the print warm for much longer than the period of solar irradiation.

Very few prints receive massive amounts of direct sunlight at close range. I'm not sure where you are getting your 50c assumption but not buying it.  

I don't know how you measured the temperature of your prints but I wonder if it was scientific enough to really know how hot the actual paper was. Measuring the air around the print isn't the same, and even 40c is pretty excessive. Certainly while short periods of time are not a problem, extended exposure to heat is. I just don't see any correlation to real world situations.

I understand the desire to test the paper itself and the bonding of the coating to the paper, but exaggerated test conditions really don't work that well. That's one of the real concerns about print longevity ... we can test the fade characteristics of the ink set, and to some degree the deterioration of other factors from UV and perhaps ozone, but simulating all the other environmental issues a print might go through is problematic.

I've done many fading tests like this over the years ... back window of my car, window of my shop, and any circumstance which allows enough sunlight to fade images quickly also subject the print to temperature extremes.  The prints always curl or sort of fall apart ... something I don't see with many decade old prints that haven't been subjected to the same treatment.

shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #15 on: March 09, 2014, 04:23:36 PM »

Not scientific but still interesting.

I think that the compatibility of the sizing and the coating medium could have an influence (does not even have to be the same "glue") but you also should count the roughness of the paper base at the bond level. Not only does a rougher surface increase the bond's surface but its geometry also dampens the expansion and shrinking forces over the total surface. A smooth paper based inkjet paper has a more uniform layer structure, say planes on top of one another that have more problems with heat/humidity expansion differences. I feared that the polyethylene barriers in RC paper would create an issue on the coating bond anyway, PE is quite inert and needs Corona treatment to create a better bond for inks and glues. Even then a weak bond. If the coating is not much more than gelatine or PVA like in analogue photo papers then the flexibility of coating will cope as long as that flexibility is kept, it will be harder when minerals are introduced in the coating like it is done in the inkjet coatings we use today. That the fiber/baryta papers are not free of mechanical wear is interesting too. The sizing compatibility should not be that different to that of the cotton papers.

I think the polythene layer is problematic for two separate reasons. Firstly, the bond with the inkjet layer is weak, allowing the inkjet layer to easily flake off or crumble. Secondly, its rigidity in comparison with the paper base causes great stresses when the paper expands and contracts with humidity; these stresses can lead to cracking or warping of the RC layer.


Quote
Your paper summary is a bit confusing. Barytes are used in papers without them mentioned in the product name and the Photo Rag Baryta is a cotton paper. There might be a relation between the roughness of the paper base (most cotton but also some alpha cellulose qualities are rough at the base) and the compensation of expansion etc. For smoother inkjet paper surfaces there is a distinction between creating them on smooth paper bases or creating a smooth surface on rougher paper bases, say only satinised after applying the inkjet coating and not twice in the inkjet paper creation. A rougher backside can give an indication though it is possible to make a paper base with one side (hot press) satinised while the other side keeps a rougher surface.

I suspect this is due to the inflexibility of the baryta layer. The paper expands and contracts with changing humidity, but the baryta layer doesn't. This causes stress at the interface between the paper and the baryta layer; given that the baryta layer is so thin, it can't take the stress and begins to crack or delaminate. The inkjet layer on top of the baryta probably holds up just fine - it's the baryta layer that fails, taking the inkjet layer with it.
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Farmer

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #16 on: March 09, 2014, 04:25:38 PM »

You presumably measured the media temperature as a spot measurement on the side away fro the glass, which could be significantly different to the surface facing the glass.  That differential, for starters, could have caused significant issues.

Those temperatures are hugely different from prints behind glass mounted on a wall some distance from the window, even if they get direct sunlight for some period of the day.
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Phil Brown

shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #17 on: March 09, 2014, 04:33:16 PM »

Very few prints receive massive amounts of direct sunlight at close range. I'm not sure where you are getting your 50c assumption but not buying it.  

There's no 'close range' when it comes to sunlight. It all comes from the same source 150 million kilometres away. If an object is receiving direct sunlight, it makes no difference whether it's 1cm away from the glass or 10m behind it. A print on a north-facing wall 3m away from the window receives just as much sunlight and gets just as hot as the same print right up against the window - just that the print on the window will be irradiated for longer than the print on the wall (due to the movement of the sun's relative position in the sky).

It's fairly logical, really. If you put a print inside a frame, you've created a close environment with minimal air circulation. Dark objects (e.g. prints) absorb much more radiation, and become much hotter than, light-coloured objects. This heat has to go somewhere. The print absorbs heat from the sun and, in turn, heats up the air in the frame. This air is trapped there and has nowhere to go - it just gets hotter and hotter.

If you don't believe me, try sitting in a small room with lots of sunlight on a hot day, with the door closed. Then do the same thing in a large room with lots of sunlight and the doors open for air circulation. I can guarantee that the small room will heat up a lot faster than the large room.

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I don't know how you measured the temperature of your prints but I wonder if it was scientific enough to really know how hot the actual paper was. Measuring the air around the print isn't the same, and even 40c is pretty excessive. Certainly while short periods of time are not a problem, extended exposure to heat is. I just don't see any correlation to real world situations.

Infrared thermometer. The same one I use for measuring body temperatures of patients, as well as measuring the temperature of heated metal. It doesn't measure air temperature - it measure temperature through the blackbody radiation of the surface.

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I've done many fading tests like this over the years ... back window of my car, window of my shop, and any circumstance which allows enough sunlight to fade images quickly also subject the print to temperature extremes.  The prints always curl or sort of fall apart ... something I don't see with many decade old prints that haven't been subjected to the same treatment.

The amount of solar radiation you get in 3 months over the spring/summer is equivalent to a lot more than a few decades of typical use.
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shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #18 on: March 09, 2014, 04:36:06 PM »

You presumably measured the media temperature as a spot measurement on the side away fro the glass, which could be significantly different to the surface facing the glass.  That differential, for starters, could have caused significant issues.

I'd strongly disagree on this. A piece of paper is thin enough that the temperature on one side is much the same as the temperature on the other side, after its been heated for a while.

Try holding a cup of coffee in a (non-ribbed) paper cup. Pretty soon, it becomes far too hot to hold.

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Those temperatures are hugely different from prints behind glass mounted on a wall some distance from the window, even if they get direct sunlight for some period of the day.

I agree. Prints - especially dark prints - mounted behind glass away from the window get a lot *hotter* than white paper mounted outside glass.

That's why the surface on my black leather sofa (well away from the window) gets to 50-60 degrees on a hot afternoon, when it is hit by direct sunlight. Trapping it behind glass only makes it hotter.
« Last Edit: March 09, 2014, 04:38:34 PM by shadowblade »
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shadowblade

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Re: Results of six-month 'window test' on inkjet coatings
« Reply #19 on: March 09, 2014, 05:06:40 PM »

I'm curious if you observe, with the matte rag papers, Hahnemuhle Photo Rag and Canson Etching Edition, any tendency for the clay-like receptor coating to become more powdery, flaky, or lose it's physical integrity or in any way. Might require some slight abuse to induce anything noticeable?
I found the test info useful, it all helps.
Thanks,
Tyler

I'm not sure. Internal stress within the receptor coating is mostly due to expansion and contraction of the paper. How the layer copes with this stress (whether by cracking, peeling or simply bending and conforming) depends on whether the layer stays flexible or becomes rigid and brittle with UV exposure. There was a lot of cracking and other problems in the papers with a rigid layer between the coating and paper (the RC and baryta papers) but none that I saw in

I think it would be a useful test to form a sheet composed purely of UV receptive coating (e.g. a 1mm-thick layer of Inkaid), allow it to dry and then see what happens when it is exposed to UV light and atmospheric pollutants - whether it retains its flexibility, or becomes stiff and brittle.

If it holds up well, an inkjet 'paper' consisting of a 1mm thick film of inkjet coating, with a white polyester mesh embedded within it for whiteness and strength, might be worth considering.

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