Seasonal Humidity Swings & Stretching Canvas

[Light Seeker]

I noticed that the canvas prints I stretched during the summer have become "loose" this winter. I'm on the Canadian prairies, and the relative humidity goes from ~50% (summer) to ~25% (winter). I assume this summer they will tighten up again.

Which season should I target for a normal, firm stretch; summer or winter? Put another way, do you take into account the humidity when you stretch a canvas and compensate for it?

Thanks.

Terry.

[MHMG]

 Humidity induced expansion/contractions in hygroscopic materials like paint (or inkjet coatings) on gesso coated canvas expand as humidity increases and contract as humidity decreases so, your expansion to a "looser" overall canvas should be going from winter to summer, not summer to winter. Hence, what seems like a loosening of the canvas may really be an indication that your canvas is actually shrinking while restrained more at specific staple points in such a way that the lines of increased tension are not uniform. This non uniform contraction could cause some apparent "waves" or wrinkles as the increased tension becomes non uniformly distributed over the whole fabric. If this is the case, there will be some areas of the artwork that will seem quite taught if you press on those areas compared to other areas that seem like they are sagging. Overall looseness throughout would be a sign of expansion not contraction, but it's hard for me to envision this situation in a summer to winter direction of humidity change.

If you can wait to observe until summer then the apparent waviness may settle again, but to avoid the problem altogether you may want to reexamine how you can stretch your canvas more uniformly when you first do it. Some paintings conservators in museums have started to back paintings with honeycomb aluminum using a hot wax to make the bond to the panel rather than continuing to use traditional "keying out" techniques with traditional wooden stretcher bars that ultimately have proven to be very hard on the artwork (i.e, resulting in preferential cracking patterns in the paint originating at the corners of the frame over time).

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

[Light Seeker]

Hence, what seems like a loosening of the canvas may really be an indication that your canvas is actually shrinking while restrained more at specific staple points in such a way that the lines of increased tension are not uniform. This non uniform contraction could cause some apparent "waves" or wrinkles as the increased tension becomes non uniformly distributed over the whole fabric. If this is the case, there will be some areas of the artwork that will seem quite taught if you press on those areas compared to other areas that seem like they are sagging. Overall looseness throughout would be a sign of expansion not contraction, but it's hard for me to envision this situation in a summer to winter direction of humidity change.

I just checked the first print I noticed this with and the sagging is uniform. There are no waves or wrinkles.

Given what you've said perhaps I simply didn't get the canvas stretched tight enough to start, and I didn't notice it until some time had passed. Or, perhaps I waited too long between coating and stretching. I recall having a print that was tight when stretched but loose a day later. Which leads me to ask if (or how much) the coating thickness is a factor wrt canvas shrinkage / expansion.

Thanks Mark.

Terry.

[petermarrek]

For years I stretched canvas, even emulsion stripped Cibas and encountered this problem,now I just mount some of my canvas prints on i/8 in. masonite using yellow carpenter's glue and rolling them in my roll laminator and then apply whatever frame treatment my custmers want. Perfectly flat prints in all seasons. Peter

[NickCroken]

I've had similar issues (Edmonton, Ab).  What I do if the canvas is just a bit saggy is slightly dampen the back of the print and heat it up with a blow dryer.  That tightens things up again.  If that doesn't work than I tap out the stretcher bars in equal directions.  I assume you are using dove tailed stretcher bars.

[DotCom Editor]

I just mount some of my canvas prints on i/8 in. masonite using yellow carpenter's glue and rolling them in my roll laminator and then apply whatever frame treatment my custmers want. Perfectly flat prints in all seasons. Peter

Interesting idea. But not at all archival, given the materials you've specified. Is there a similar solution that would use archival mounts and adhesives?