The trade off of any clear finish is finding the right combination of hardness and flexibility. Too hard, and it winds up fracturing over time when it contracts and you wind up with craquelure. Too soft, and it is gummy and sticky. That's what has impressed me about Glamour II, is that it has a very nice balance of the two. I know from decades of painting experience that water borne finishes that are inherently glossy, meaning that they do not have flattening agents mixed into them (usually talc), stay soft and impressionable for quite some time. The paint manufacturers say that semi-gloss and gloss acrylics have a cure time in excess of a month before reaching maximum hardness. Heat accelerates the cure, but exacerbates the softness and stickiness problem until a full cure is reached, if you've ever seen one of these finishes after being left in strong direct sun.
With luck, you will find that the problem with the Rosco product goes away as it reaches a full cure. I've used their scenic paints for a very long time, and they have a great reputation for quality products. Unfortunately, I haven't been willing to experiment with something that we really won't know about for years down the road, when selling a product that I'm promoting as archival. I feel much safer using one of the products tested and promoted for canvas art coatings until there is a wider consensus about the alternatives. I know of a local fine art printer who experimented with third party inks in his Epson and paid the price in only a year's time, and would personally dread a phone call down the road when I heard from a client about one of my pieces failing in some way, as a result of me going off the beaten path. YMMV
This may just be an issue of folks not packing or storing their finished work properly. I never put anything face to face without something neutral in between, usually a piece of foam core. I did spray all these canvasses, let some of them dry for as little as 2-3 hours, then stretched them and had them hanging outside under at tent in 98 degrees high humidity for 2 days. Packed them in cardboard boxes, 2 to a box, back to back, and then they sat in an enclosed van this morning for a few hours before I got them out (tired!). Result? They look great. No scuffs nor marks. Some of the canvasses need to be tensioned a little.
Regarding the Rosco materials, I'm going to put some of these in the direct sun and do some tests. I have numerous friends in stage, TV and film production and everyone - everyone - vouches for the reliability, consistency, and quality of the Rosco coatings. That's why I'm using it. As far as longevity, Rosco has been around a whole lot longer producing products for much more quality critical customers than Breathing Color or Glamour anything, and we won't know the real, actual archival qualities of any of this stuff until the 200-300 years has actually passed. I'll take Rosco's track record and reputation, but if I have any problems or if everything continues to look great, I will definitely report back here.
I don't market anything on canvas I'm spraying goop on as "archival." The whole reason I'm doing canvasses is to use the deep profile stretchers to cut out the framing and glass from my photos to sell to a different buyer. Any photo not behind glass I have a hard time representing as archival. If someone is that concerned about archival qualities, I'm prepared to make a print on ph neutral paper, no coatings, and frame behind glass with museum quality materials. But they are going to have to pay more, a lot more, for that product than for the convenient ready-to-hang work on canvas. For me the coating is about a layer of protection from the elements and to make the canvas "cleanable" and "dustable" more so than to make it archival.
That said, if I have any probems, I'll report back here. I had a friend who did set design for the Met, and the Rosco paints / coatings carried his highest recommendation. Along with virtually all my other pals doing set work. I got the initial idea from Nollendorfs here, then followed up with people using the stuff What really got me moving in that direction away from the Breathing Color's and Clearstars that the only way I could find to get them was off the web. Rosco is more convenient and affordable because I have at least one local supplier. And it sprays great through that cheap Wagner sprayer.
I don't have much experience spraying canvas, but I have years of experience packing, unpacking, shipping and displaying art. I would say the surface of any canvas, sprayed or unsprayed, should not be coming into contact with the front or back of another canvas. Ever. Issues of sticking likely aren't so much a problem with the coating as a problem with one's packing or storage method.
I'm in the south with a south facing porch. Think I'll do 4 prints of the same image, all sprayed with Rosco Clear. One in a dark box. One in a South facing window. One just hanging on a wall. And one tacked up exposed to the sun and elements hanging right off the porch! I'm printing on Sunset Select Matte Canvas. I don't know if the Sunset Select Matte Canvas has OBA's.
Thanks to everyone here for all the help, advice and suggestions.