gentle medium
Start with a gentle medium if you are uncertain. If you are unsure how the material will withstand sandblasting it is best to choose the gentlest medium and work your way up. Walnut shells are one of less abrasive sandblasting media you can use and are completely biodegradable, so there are no concerns about environmental impact.
Corn cob is also biodegradable and will not etch the material being blasted. Pumice is the softest of all the blasting media. It is often used to remove paint from soft wood.
Sodium Bicarbonate or Soda blasting is our preferred process for delicate surfaces like fiberglass and thin aluminum such as airplanes. This is a very mild method and creates no heat so warping is not an issue!