CREATE TABLE table_17974 ("Value" TEXT, "Diameter" TEXT, "Thickness" TEXT, "Mass" TEXT, "Composition" TEXT, "Edge" TEXT, "Obverse" TEXT, "Reverse" TEXT, "first minting" FLOAT, "issue" TEXT, "withdrawal" TEXT, "lapse" TEXT)

What material is made with a rounded, plain edge?
SELECT "Composition" FROM table_17974 WHERE "Edge" = 'Rounded, plain'
SELECT "Composition" FROM "table_17974" WHERE "Edge" = 'Rounded, plain'