Common problems encountered with improper solvent selection

It is necessary to control evaporation of various volatile components of the lacquer in order to prevent 'Chilling', 'Gum Blush' and 'Cotton Blush'. These features are described below.

'Chilling' refers to the formation of an opaque film and is attributable to the lowering of the temperature of the film and air near the film to below the dew point. It is caused by the high rate of evaporation of a highly solvent from the solution. The problem can be remedied by increasing the proportion of the 'medium boiler' in the solvent mix and butanol is particularly useful for this.

'Gum Blush' and 'Cotton Blush' occur when either resins or nitrocellulose respectively are precipitated from the lacquer. 'Gum Blush' is caused by too rapid an evaporation of solvent for the resin which eventually is precipitated out and similarly 'Cotton Blush' is caused if at any point during evaporation of solvents the dilution ratio is exceeded. 'Blushing' can be avoided by using a small proportion of high boiling solvent which dissolves both nitrocellulose and resin.