Since it has been tried to substitute zinc oxide for white-lead in painting, researches have been made to replace litharge as a drier by a substance free from the inconveniences which caused the abandonment of white-lead. If sulphuretted hydrogen impairs the whiteness of painting done with white-lead, it is not logical to employ a lead drier with zinc paints, because the latter substances will lose their advantage of not becoming dark. Several metallic oxides and salts, especially zinc sulphate, manganese oxide, and umber, have the property of combining with oils, which they render drying. To these may be added the protoxides of the metals of the third class, i. e. iron, cobalt, and tin. But these oxides are very unstable and difficult of preparation; hence it became desirable to discover some means by which they might be combined with bodies which would enable them to be prepared cheaply, and at the same time leave unimpaired their desiccating powers. Moreover, it is acknowledged that driers in the dry state are preferable in many respects to drying oils.

Following are some of the recently-introduced driers: -

(1) Cobalt And Manganese Benzoates

Benzoic acid is dissolved in boiling water, the liquid being continually stirred, and neutralized with cobalt carbonate until effervescence ceases. Excess of carbonate is removed by filtration, and the liquor is evaporated to dryness. The salt thus prepared is an amorphous, hard, brownish material, which may be powdered like rosin, and kept in the pulverulent state in any climate, simply folded in paper. Painting executed with a paint composed of 3 parts of this drier with 1000 of oil and 1200 of zinc-white, dries in 18 to 20 hours. Manganese benzoate is prepared in the same way, substituting manganese carbonate for that of cobalt. Applied under similar circumstances, it dries a little more rapidly, and a little less is required. Urobenzoic (hippuric) acid is equally efficacious.

(2) Cobalt And Manganese Borates

These salts also, in the same proportions, are found to be of equal efficacy. The latter is extremely active, and requires to be used in much smaller proportions.

(3) Resinates

If an alkaline resinate of potash or soda be dissolved in hot water, and this solution be precipitated by a solution of a proportionate quantity of a cobalt or manganese chloride or sulphate, an amorphous resinate is formed, which, after being collected on cloth filters, washed, and dried, forms an excellent drier.

(4) Zumatic (Transparent) Drier

Take zinc carbonate, 90 lb.; manganese borate, 10 lb.; linseed-oil, 90 lb. Grind thoroughly, and keep in bladders or tin tubes. The latter are preferable.

(5) Zumatic (Opaque) Drier

Manganese borate, as a drier, is so energetic that it is proper to reduce its action in the following way: - Take zinc-white, 25 lb.; manganese borate, 1 lb. Mix thoroughly, first by hand, then in a revolving drum; 1 lb. of this mixed with 20 lb. paint ensures rapid drying.

(6) Manganese Oxide

Purified linseed-oil is boiled for 6 or 8 hours, and to every 100 lb. boiled oil are added 5 lb. of powdered manganese peroxide, which may be kept suspended in a bag, like litharge. The liquid is boiled and stirred for 5 or 6 hours more, and then cooled and filtered. This drying oil is employed in the proportion of 5 to 10 per cent. of the zinc-white.

(7) Guynemer's

Take pure manganese sulphate, 1 part; manganese acetate, 1 part; calcined zinc sulphate, 1 part; white zinc oxide, 97 parts. Grind the sulphates and acetate to impalpable powder, sift through a metallic sieve. Dust 3 parts of this powder over 97 of zinc oxide, spread out over a slab or board, thoroughly mix, and grind. The resulting white powder, mixed in the proportion of 1/2 or 1 per cent. with zinc-white, will enormously increase the drying property of this body, which will become dry in 10 or 12 hours.

In using driers, observe that you (1) do not employ them needlessly with pigments which dry well in oil colour, (2) nor in excess, which would retard the drying, (3) nor add them to the colour until about to be used, (4) nor use more than one drier to the same colour, (5) nor use any at all in the finishing coat of light colours.