Feature October 2014

Baxter’s Oil Colours

Mr Fred W. Seeley who for many years superintended the production of colour prints from the press of Messrs. J.M. Kronheim & Co., who were licensees of George Baxter, gave us an insight into why varnish was used as a medium for the colour pigments and how this varnish was made.

Up to the time George Baxter invented his process, practically all colour illustrations of any importance, were produced by colouring up engravings or lithographs, by hand work in water colours.

When pigments are ground in water, they never form a body or show any brilliance and it is not possible to ink in a block successfully. Therefore an oil was used, which, when treated, would form a medium, stiff enough to carry and sustain the pigment ground into it. The best oil for this purpose was linseed oil, and George Baxter, like all the earlier printers, made their own varnish from linseed oil.

Linseed oil contained about 33% of fatty substances, 30% albuminous matter, 34% water and 3% mineral ash, and out of the 33% of fatty substances, only 80% is of real use as varnish. The method adopted in the early days was to part-fill a cauldron with linseed oil and boil the contents. The heat soon gets rid of the water, and with constant stirring the oil begins to emit heavy fumes, these are ignited and allowed to burn for a given time. By this means the albuminous matter, and the non-drying properties contained in linseed oil, are burnt out, and what might be termed the gummy matters remaining, are reduced to a scum, or ash upon the surface, which is then skimmed off. When the oil has boiled and burned down to a considerable extent, the flames are extinguished, by placing a lid over the cauldron. A sample can then be tested, and if the varnish is too thin, it is again boiled and burned. The process is continued, for the various degrees of consistency required, as what is termed the “thickness” of varnish, varies for the class of ink to be used.

Generally this varnish making was done over the kitchen fire, and with boiling oil set alight, to burn off the heavy fumes, it was not an uncommon thing for fires to take place, often with dire results, and insurance companies in those days often refused to insure against fire.

This finished varnish dries with the pigment on the surface of the paper, rather than drying into the paper which would leave the pigment in a dust which could easily be rubbed off.

Various ingredients were added, at times, to assist in drying the inks more rapidly.