White glue restores old decals
I purchased a 20 year old Hasegawa P-51 kit at a hobby show and discovered the decals had been probably stored in a humid environment. The decals were firmly affixed to the backing paper. Needing to use at least a few of the decals, and with nothing to lose in an experiment, I experimented with a decoupage technique. I simply painted 3-4 thin coats of thinned Elmer's glue over the decals. The glue was randomly thinned from 10-25%. While it helps to trim closely to reduce the excess dried glue film, any excess glue is easily brushed away with a wide bristle brush upon application. Simply cut out the decal and soak as usual. At 30 seconds soaking the white glue turns cloudy. At 60 seconds the decal is ready to slide from the backing. My times are likely excessive, less time will work. Apply the decal to the kit and smooth with a wide flat brush. The excess white glue is brushed away. Clean the brush with water and smooth again to remove any additional excess. When the decal is dry, cover with a sealant such as Future. I did not notice any discoloration or fogging or excessive thickness due to the white glue. Sometimes we think a solution has to be complicated or exotic to work properly. Or perhaps it is something simple and basic.