My goal is to have a goal

The roundabout pattern of having a problem, trouble shooting and then solving the problem has been my theme with my photo fresco experiments over the past five or so years. It's addicting in that solving the problems is like having immediate goal, something to work on, so each time I get one issue out of the way another pops up. Lately I've gotten past most of my old issues with durability and embedding images and I've even gotten the cost of materials for a medium sized piece down to less than $20, which means I don't have any immediate goals besides production and content. Oh, what to do? My last small set of test pieces were made in a batch of 5 molds with a variety of random images added to the mix. I have gotten a final surface using epoxy that imitates brick without having a glossy top surface. The image area is clear with a spray painted stencil image painted and in some cases molded into the pieces creating a relief effect. The light can shine through the clear areas creating an effect that can change depending on the placement of the final piece. I've attached and reinforced the epoxy shell to the frame with fiberglass cloth and tape. These pieces should survive well if weathered or left in dank or rough conditions, with the exception of high heat, over 130 degrees. I did not fill the backs with gypsum plasters or cement, so they are light enough to hand and could very well survive a good fall of six feet or more without significant breakage. This leaves the only problem to be solved is the clear areas will turn yellow over time with exposure to the sun. I found an early piece laying in my yard, weathered and the coloring behind the clear epoxy was protected by the top surface. Even though the epoxy had yellowed the colors kept this effect from overshadowing and distorting the colors. The yellowing was more dramatic in areas where there was a white substrate. The bigger problem with this earlier piece was the plaster below the image was eaten away and dissolving from laying in the dirt. Also it was fragile as I dropped it back to the ground it snapped. Thus I am confident that two of these longstanding issues with may materials are solved, like the fragility and top surface yellowing except for the areas in my pieces that are clear. The biggest question is how much yellowing will occur as I don't think all the additional coatings in the world will do anything more than add work, cost and change the finished look and feel that I am currently happy with. The yellowing of epoxy is acceptable to me in that I am thinking of it in the same way as how "clear" appears in nature. Amber is a very protective transparent surface that last forever and even diamonds are yellow to some degree. Hopefully the yellowing in epoxy is not indicative of an internal breakdown of the strength or chemical structure that makes the epoxy durable. Next goal please.