WTF is resin anyway?
It is basically a strong & durable plastic that I mold into cool pieces!
In my experience, resin can withstand strong sunlight and heat. Avoid excessive heat though to help your piece last a lifetime!
If your piece gets a little dusty over time, simply wipe with a microfiber cloth with a spritz of rubbing alcohol, or you can hand wash with dish soap and let it dry.
For your ashtray, a simple wash with soap and water should keep your piece looking new! Again, in my experience, putting out blunts & joints directly into an ashtray rarely caused any burn marks but take gentle care of your new baby!