Proofing, what is proofing?

mold opening means making a mold and starting to dry.

these nouns are often used in the general printing industry. For example, to print a batch of color pages, it will first sample, that is, print a copy first. If the customer is satisfied, it will open the mold, that is, make the mold and start printing. Because it is expensive to make a mold (copperplate printing, etc.), the more copies are printed, the cheaper the average price is.