After casting multiple times into the Delft Clay molding material (s), it begins to lose some of its adhesive qualities. Now you can refresh your used Delft Clay by adding, just a little at a time, some Delft Clay Extra additive. You can also cast into Delft Clay Extra alone and, because it is finer than regular Delft Clay, obtain even better castings.Provided in a bag containing 2.2 lbs. of Delft Clay Extra. Made in Holland.