i wondered if anybody had any possibe advice on how to seal/varnish hand drawn shrink plastic items (sharpies/pencils used) - ?
most products i have tried so far tend to make ink run & i was hoping for any tips.
My years as a chemist gives me a bit of insight to this but I have never tried shrink plastic so I am coming at this for a chemistry point of view. The ink in sharpies or permanent markers is solvent based to keep it runny until used when the solvent can evaporate, most varnishes and sealants are solvent based to keep them runny until used when the solvent can evaporate. So when you apply the varnish to the pen it redissolves it and it runs as you have discovered because it is a solvent/ solvent based system. You need to switch to a water/ solvent based system so either a water based sealant with the pens you have or switch to non permanent markers (designed to desolve in water) and use a solvent based sealant (eg clear nail polish).
With pencils you are leaving a thicker layer of particles behind than with ink so when you shrink it the layer gets thicker still and then flakes off due to lack of adhesion to the plastic surface. Any sort of sealant should be fine so long as you get to it before the flaking occurs and don’t disrupt the pencil layer in the process of sealing. A spray sealant would probably work best in that case.
Science lesson over and I hope it was helpful.