Enhancement of visibility of structures in marly chalk: modification of the Bushinsky oil technique

The outwardly monotonous appearance of white chalk is deceptive, yet the several techniques that have been applied to enhance visibility of hidden structures have all had limited success. A technique published by Bushinsky in 1947 produces excellent results with chalks containing a trace of clay minerals. Bushinsky's technique involves incomplete impregnation of chalk samples with light machine oil, but still better results were obtained by lightly brushing oil onto smoothed surfaces of chalk. The heightened contrast of the structures thereby achieved can be still further increased photographically by use of high contrast line copy film. The results obtained are compared with those using fluorescence by ultraviolet radiation or by merely wetting the chalk. Both contrast and resolution are better with oil than with water or ultraviolet.