SilverStone is a non-stick plastic coating made by DuPont.
Released in 1976, this three-coat (primer/midcoat/topcoat) fluoropolymer system formulated with PTFE and PFA produces a more durable finish than Teflon coating.
As of 1980 Dupont required that the pans carrying the brand be a heavier weight than others on the market.
[1] The process for creating Silverstone cookware begins by sandblasting the products which creates an uneven surface that encourages adherence.
Then a primer layer of Teflon is sprayed on and after it is baked at high heat to "a secure mechanical grip.