From the manufacturer: Our American Clay color pigments are placed in individual packs that are pre-measured to be added to one 50-lb. bag of plaster. Each individual color pack will vary in weight depending on how much pigment is used to create that specific color. American Clay color pigment packs contain naturally occurring mineral pigments, which means they are resistant to UV light and fading. Our pigments are made in batches and every pack will have a batch number printed on the label. We do recommend using color pigment packs from the same batch. If this is not an option, simply blend clay plaster that has been tinted with two different batches of pigment in order to unify the color for consistency. If using color pigment packs with Enjarre plaster, a ratio of 1-¼ color pigment packs to one 80-lb. bag of Enjarre is used. The 1-¼ color pigment ratio will closely match standard Loma colors.