Decal Shelf Life

One thing I now do is to scan all kit decals when I start building.  As I become more experienced with inkjet decals, I find I can use that copy to make replacements for any of the originals that fail.

Also, when I begin decaling a model, I first find a decal that will not be used.  Most decal sheets have extraneous printing, like copyright or trademark notices, or kit identification printing, that will suffice. I then cut out that area and dip in water to see if it will shatter. If it does, I then coat the whole sheet with aftermarket decal film.

I also like ziplock bags for storing decals.

That depends on the brand of decals. I've got usable decals that are well over thirty years old. Tamiya decals, old school Monogram decals, and old school Matchbox decals have very thick film and still are usable.

Some aftermarket ones are more fragile because they have very thin carrier film. If stored properly, they can last for years and years. And if they look dried out, spraying a coat of clear coat will make them usable.

I have a loose leaf 3 ring binder with clear page protectors. The binder has dividers so I can catagorize decals by type; i.e. 1/72 scale armor, 1/35 scale armor, aircraft, sci-fi, etc. I put loose leftover decals in ziplock bags separating them by type, like WW2 German markings, white US stars, etc.

So if I go to my 1/35 scale armor tab, inside the page protector is several ziplock bags with Soviet, US, German and another with miscellaneous (like Japanese, British, Italian, etc. markings)

I also sometimes put the kit decals into small ziplock bags when they are loose in the kit box and not sealed. Helps keep them fresh.

They can go bad, but I have sets of Microscale decals from the mid 80's that are still viable. I've also used Monogram Nascar decals that were over twenty years old. It just depends on the sheet and how you store them. I've been putting them in ziploc bags for years, and keep them in the house with the air conditioning and heat.