A putty rubber is a type of eraser that is used to remove and lift the pigment of charcoal, pastel and pencil. It is intended to be shaped, moulded and dabbed rather than rubbed. The main purpose of a putty rubber is to remove pigment however it can also be used to slide and blend pigment to create different effects.
A putty rubber is also known as a kneadable Art Eraser. They are often the same thing but some kneadable Art Erasers are less soft and malleable than putty rubbers.
The more pressure you use with the putty rubber, the more pigment can be removed. The putty rubber can completely remove all pigment depending on the grain of the paper and its absorbent qualities.
Some papers with a grain or ‘tooth’ may retain some pigment and complete removal may not be possible. The putty rubber is an inexpensive and versatile tool and I think essential for use with charcoal and pastel.
Some sensitive tonal drawings can be created with charcoal and a putty rubber, one way of working this way would be the subtractive technique. In this technique you cover your paper with pigment and create the drawing by removing pigment with erasers such as a putty rubber and other soft erasers.
The pigment is dabbed away with the putty rubber and it will be absorbed by the rubber. Having said that you can also scrape and move the pigment around with these erasers.
So why not give the putty rubber and the subtractive method a try? It is an interesting tool to work with and drawing will look different to pencil or charcoal that is used in the more conventional way.