It is a well-known fact to the trade that the evolution of these flat finishes is due to a great extent to the efforts of the manufacturers of lithopone, both here and abroad, to find a greater market for this white pigment than that derived from the linoleum and oilcloth and shade cloth makers. That the efforts have been successful is proven by the favorable reception this material has received and the enormous output since the first brand was placed on the market by a certain varnish house. Quite a share of the credit for its success is due to the availability in late years of China wood oil varnish preparations and the progress made by petroleum refiners in perfecting the heavy gravity petroleum spirits generally known as turpentine substitutes. The ordinary 62 degrees petroleum benzine would not have given the flat finish, and would have made the paint set so rapidly that it could not have been spread, while the addition of more oil would have tended to gloss up. Again, for a certain period the cost price of turpentine almost prohibited its use. Several years ago a number of varnish makers issued formulas for paint makers showing them how to prepare flat wall finishes by using the liquid supplied by them for the purpose. The results obtained by following these formulas varied considerably and even the batches made from time to time did not always turn out uniformly. One of the formulas in question, issued by one of the most prominent firms of varnish makers in the United States with a branch in Canada, is as follows: - "Paste base to be ground on suitable mill: -
pounds G. S. lithopone (brand specified);
pounds XX New Jersey zinc;
pounds china clay, bolted English;
pounds bolted whiting;
pounds flatting grinding liquid;
Blued with 1 ounce dry ultramarine blue. To the above add in a suitable mixer 4 gallons of a mixture of 46 parts by volume of turpentine substitute and 4 parts turpentine, producing a batch of 18 gallons weighing 16 1/2 pounds each." What benefit the 4 parts of turpentine would have with 46 parts heavy petroleum naphtha is difficult to understand. The flat finish made in this formula did not work as well as the following given out by another firm of varnish makers: - "Grind on a water cooled mill these ingredients: -
pounds G. S. lithopone;
pounds XX horsehead zinc;
pounds bolted English china clay;
pounds English cliffstone white, bolted;
pound dry ultramarine blue;
pounds flatting liquid (8 1/2 gallons);
276 1-16 pounds.
Result: - 19 gallons flat paint when thinned with 4 1/2 gallons turpentine substitute or with 2 1/4 gallons each of this and spirits of turpentine." This paint works fine, dries dead flat without sheen, but cannot be cleaned by scrubbing with water containing any alkaline soap, soap powder or ammonia.
A washable flat wall paint which, however, shows a slight sheen, that has been made and sold for years successfully, is composed of the following: - Grind fine on a good white paint mill: -
pounds green seal lithopone (normal);
pounds American Paris white (bolted);
pounds zinc resinate, powdered;
pounds refined or bleached linseed oil;
pounds spirits of turpentine;
pounds turpentine substitute;
The zinc resinate serves as drying medium and should be ground fine in part of the oil before it is added to the batch, or fused resinate of zinc may be dissolved by heat in the oil and so added. The idea of using zinc resinate instead of manganese resinate is because the latter makes whites dry out rather pink. To every 75 pounds of this paste base use either 10 pounds of turpentine substitute or equal parts of this and pure spirits of turpentine. Result: - Five gallons of flat wall paint of very good body weighing 17 pounds per gallon.
Although some interested parties assert that a good flat wall finish can be produced only by the use of lithopone, it has been demonstrated that such a material can be made by using zinc oxide and inert base. Of course, zinc oxide lacks in opacity in comparison with white lead or lithopone, but under certain conditions it becomes necessary to sacrifice economy to other considerations. Lithopone white is liable to become discolored even on interior walls from the effects of moisture and glaring strong light, while pure zinc oxide, free from sulphur, is unaffected. There has been a belief in paint making circles that zinc oxide cannot be flatted as can white lead or lithopone, but when it is considered that zinc oxide with the proper white base requires more vehicle for grinding and thinning than lithopone and much more than white lead, it stands to reason that only the right selection of base is required. A very good base for such a flat wall finish will be found by grinding equal parts of American zinc oxide and precipitated barium sulphate (blanc fixe) in a flatting liquid that has given good results with lithopone, thinning the resulting paste base with a good substitute turpentine, and if this should set too quickly for good flowing and drying without laps, add sufficient bleached linseed oil to overcome the deficiency. The blanc fixe may be replaced by equal parts of floated barytes and magnesium silicate, but to increase the percentage of zinc oxide in order to give better opacity would not work out satisfactorily.
Interior Flat Enamels that are found on the market and many of which are imported from abroad are really higher priced flat wall finishes, selling at a figure out of all proportion to their actual value or cost. One of these can be produced on the following basis: - Grind 80 parts by weight of condensed French zinc white, green seal, in a vehicle composed of 10 parts of varnish made from white kauri gum (known as XXXXX) with only 10 gallons of oil to 100 pounds of gum), 3 parts of palest lithographers' varnish and 10 parts pure turpentine. This will produce 100 pounds soft paste base. Let it stand for forty-eight hours covered with some turpentine to keep from skinning over, then thin down with 24 pounds by weight of turpentine to the 100 pounds by weight of paste. This will give 7 6-10 gallons of material weighing 16 1/4 pounds per gallon. By grinding calcined borax in varnish or pale oil and turps and adding as much as constitutes one-half pound of dry borax to the above batch, it will tend to make the material dead flat on drying. These flat enamels may be tinted to any desired effect with colors ground in oil if only small portions are required, otherwise the colors used should be ground in japan and thinned with turpentine.