An apparatus and a method for determining a quantity of material

A method of determining characteristics of a build material, comprising:

• obtaining a first quantity of a first build material;
• determining, for the first build material, the proportion of non-marked build material and marked build material;
• determining, based on the determined proportion, a first quantity of the first build material to be combined with a second quantity of a second build material to produce a third quantity of mixed build material having a predetermined proportion of marked build material;
• and
• generating the third quantity of mixed build material.

A non-transitory computer readable storage medium encoded with instructions, executable by a processor, comprising:

• instructions to:
• determine, for a first material, the proportion of non-marked material and marked material;
• determine, based on the determined proportion, a first quantity of the first material to be combined with a second quantity of a second material to produce a third quantity of mixed material having a predetermined proportion of marked build material;
• and
• generate the third quantity of mixed build material.