Resin powder is a light yellow powder used on a lithograph plate to hold the ink or coloring material and to protect the lines on the image from the acid of the platemaking solution. It is made of residual resin (resine in French) left over after distilling the volatile oil (turpentine oil) from crude turpentine (balsam), and is resistant to acidity.
Soft cloth or cotton wool is used to rub the resin powder gently over the image, which has been drawn on the stone or aluminum plate (with lithographic crayons, tusche, printing ink, etc.), so that the powder attaches itself to the image and makes it acid-resistant. Acid resistance is enhanced by also coating the plate with talcum powder, which plays a similar role, to ensure that the image is protected against the acidic platemaking solution.