From intense hues to pastel tones, Amaco Underglaze Chalk Crayons can be used as is, sharpened for fine detail or dissolved in water for painting or spraying. Amaco Underglaze Chalk Crayons are safe to use as they are also lead free The maximum firing temperature is Cone 10 for the following: Black, Brown, Dark Blue, Dark Green, White, Gray, and Medium Blue. The maximum firing temperature is Cone 5 for the following: Turquoise, Yellow, Dark Brown, Blue-Green, Light Brown, Medium Green, and