In photo printing gasfastness is a term used to describe the durability of printed photos and how well they stand up to exposure to elements in the air after printing. Poor gasfastness of a print may show swelling of the paper, or changes to the print when handle or exposed to elements in the air. Gasfastness is determined by how ink pigment particles bond to the surface of the paper, so each printer manufacturer will have a different gasfastness depending on the paper you use to print. While the term is used as a measurement, there is no real formula to determine gasfastness.
Compare with lightfastness, the durability of a print when exposed to light.
