When i buy second hand models i ussualy find the decals yellow, because the glue on the decals is old and dried. thats most of the time no problem because you can find a lot of new replaced decals set for any type of aircraft.
but what to do when there ar no new set of the kind you want. Are there any tricks to give the old decals an new life. Or do the companies have a service desk where you can order new decals for the old boxes. i tried it once at the revell company it work then. but i can’t find any adres of hasegawa or other companies.
I’ve seen a tip on this forums saying it’s best to put it in a plastic zip-lock back, tape it to a window exposed to sunlight and that should do the job.
Haven’t tried it myself (and won’t try to take credit for the tip - just can’t remember who posted it!)
The recommended approach is to put them face out in a window that gets a lot of sun. That bleachs out the yellow. It will take some time, like weeks or even months. Then, I’d check one of the decals on the sheet to see if it stays intact when you try to apply it. If it cracks or breaks into pieces, then you need to recoat the sheet with something like Future or Microscale Liquid Decal Film.
If time is an issue for you, then trimming around the decal to remove the yellow helps.
Some of the decals I have placed in the window have come close to looking new, but not quite, so I trim the carrier film away as required.