Читать книгу The Mixing of Colours and Paints - F. N. Vanderwalker - Страница 21

Table of Contents

Opaque Colors.—These are such as hide the surface more or less completely.

The blacks are the most conspicuous, of course, in this group.

In the red group of tinting colors for house paints all cover well; venetian red, Indian red and American vermilion hide the surface very well.

Among the blue pigments all are quite opaque, except when mixed thin for glazing and staining.

Of the yellows, the chrome yellows being made on a white lead base, are the most opaque. In fact, the other yellows are commonly used as glaze colors because they possess a degree of transparency. Yellow ochre, except in the high grades of French ochre, is rather opaque and too muddy, as the decorator puts it, to be used for glazing or mixing stains.

Greens are all opaque, yet they are transparent enough in most grades to be used for glazing when mixed thin.

Browns are also fairly opaque when finely ground and used in a thick film, but all are excellent glaze colors, because of their degree of transparency when mixed thin.

White pigments which are really opaque are limited in number. White lead has held first place in the matter of opacity for hundreds of years and its many virtues may keep it in first place indefinitely.

Of recent years titanium oxide has made claim to honors as the most opaque white pigment, but its case has not yet been fully substantiated as an all-around equal to white lead.

Zinc Oxide has held second place for opacity among white pigments suitable for outside painting and it has held first place in the matter of fineness for years. It is not as opaque as white lead, however.

Then, considering only the quality of opaqueness and not general utility as a paint pigment, china clay and whiting, silica and barytes are less opaque white pigments, but are very useful for some purposes in interior decorating.

For interior wall paints, window-shade paints and enamel undercoaters, lithopone has first claim to popularity, because of its very great opacity and moderate cost. It is not suitable for exterior paints, however. It is quite likely that titanium oxide will find its greatest field in the manufacture of interior flat wall paints because it is a very opaque pigment.

Transparent Colors.—These are not really transparent in the sense that glass is transparent, but they are semi-transparent when mixed thin. The glaze colors listed in Chapter II, and especially the lake colors and aniline colors are the best examples of the transparent class, but even the commonly good grades of tinting colors for house paints are satisfactorily transparent for some jobs of glazing, mottling, blending and Tiffany finish.

For mixing stains, only the transparent colors are suitable. The aniline colors, being especially transparent, are very fine for both staining and glazing.

The Fading of Colors.—Among all the colors used some are very permanent, some fairly permanent and others are quite fugitive when placed in strong light or subjected to the elements on exterior surfaces. And it should also be remembered that many colors which prove quite fugitive and unsatisfactory when used for the wrong purpose are really suitable and satisfactory when used for the purpose for which they were manufactured. For instance, the beautiful lake colors made for superfine automobile painting and to be protected by many coats of varnish, would not give satisfactory service if used to tint outside paint. Bright colors made with Prussian blue, chrome green and certain anilines will not hold their colors long in direct sunlight, yet there are no more permanent colors of their kind to take their place. If judgment is shown about using fugitive colors, placing them out of strong light or on interior surfaces, they are completely satisfactory.

Earth colors such as venetian red, raw and burnt umber, raw and burnt sienna, yellow ochre, and some few others are, generally speaking, more permanent than chemical colors like Prussian blue, chrome green and chrome yellow; but, as stated, the latter are sufficiently permanent for the purpose of house decorating, and there are no others to take their place. If blues and greens are to be used for exterior exposure, mix them with earth colors to increase their permanency; that will dim their brightness, but when added to white or black, pleasing tints and shades are secured.

Following is a tabulation of colors arranged according to their permanence in light:

NON-FADING
Raw Sienna	Vandyke Brown
Burnt Sienna	Venetian Red
Lamp Black	Chromium Oxide Green
Ivory Drop Black	Toluidine Red
Carbon Black	Yellow Ochre
Black Oxide of Iron	Tuscan Red
Indian Red	Vermilion
Raw Umber	Ultramarine Blue (except when used with white lead)
Burnt Umber	Cobalt Blue
FAIRLY PERMANENT
Chrome Green, Light	Chrome Green, Dark
Chrome Yellow, Light	Chrome Yellow, Orange
Chrome Green, Medium	Cadmium Yellow
Chrome Yellow, Medium	Para Red (aniline)
FUGITIVE
Prussian Blue	Carmine
Antwerp Blue	Crimson Lake
Chinese Blue	Scarlet Lake
Dutch Pink	Purple Madder
Red Lead	Madder Lake
Aniline Reds (except Toluidine)	Rose Madder
Indigo	Purple Carmine
Indian Yellow	Violet Carmine
Yellow Lake

Chemical Reaction of Some Colors.—Certain combinations of colors and pigments result unfavorably because they set up chemical reaction which should be avoided. The principal ones which a decorator is likely to encounter are the use of ultramarine blue, cobalt blue, English vermilion and Chinese vermilion, with white lead. In the making of ultramarine blue and cobalt blue, sulphur enters the process and this reacts unfavorably upon the white lead, turning it from lead carbonate, which is white, to lead sulphide, which is black. When you cannot produce the blue tints or shades wanted without using ultramarine blue, use oxide zinc for the white pigment instead of white lead. Prussian blue, Antwerp blue, and in fact all blues except ultramarine and cobalt, may be used satisfactorily with white lead.

Ultramarine and cobalt blues, however, possess the valuable trait of being proof against active lime, soda and alkali in new cement and plaster walls. Consequently, tints and shades made with these blues do not fade and spot as do tints and shades made from Prussian blue when used on new plaster and cement surfaces.

Until such surfaces have aged, which requires a matter of months, their caustic properties are still active, and will cause these colors to change to a spotty appearance and fade out in places. A new surface of this kind can be chemically aged by brushing on a solution consisting of ten or twenty parts zinc sulphate to eighty or ninety parts water.

English, French and Chinese vermilions being compounds of mercury and sulphur should not be mixed with white lead, chrome yellow, orange chrome or American vermilion. Such vermilions have a tendency to turn black when mixed with lead and lead colors.

Mercury vermilions should not be mixed with copper colors like Emerald green (Paris), verdigris green and malachite green if unfavorable chemical reactions are to be avoided. American vermilion is a basic chromate of lead resulting from the same process, generally speaking, as chrome yellow, and it may therefore be used where Chinese and English vermilions are not advisable.

Indian red as made today is a chemical color produced from iron and steel scales removed by the use of certain acid liquors in the mills. If the acid is not completely eliminated, paint made from Indian red for use on iron and tin surfaces will cause rusting instead of protecting such surfaces, for which purpose the paint is used. Careful manufacture, however, completely eliminates or neutralizes the acid. Venetian red, being manufactured in substantially the same way, is likely to possess the same characteristics.

Bleeding Colors.—In past years rather large quantities of aniline red stains have been used for producing mahogany finished wood trim in homes and for furniture finishing in mahogany. Some of these mahogany stains were of the para red class of anilines, which have exceptional penetrating ability. As long as the finish of the wood remained mahogany no difficulty occurred, but when the finish is changed to white paint, white enamel or light tints in paint or enamel, these para red anilines soon penetrate the new finish and turn it to a clouded pink color.

In some of the simpler cases the aniline can be sealed up by brushing on a coat or two of shellac. In some cases a coat of flat black mixed from coach or ivory black ground in Japan and turpentine will stop the bleeding. In the most radical cases nothing but a coat of aluminum bronze paint has been found effective. The enamel or painted finish, of course, is produced on top of the bronze coat. In some cases decorators have stripped off the old finish down to the bare wood and washed the wood thoroughly with alcohol, and later with liquid varnish remover, in order to remove all of the original stain possible from the pores of the wood. After this stripping-off process the new finish is built up on top of a coat or two of shellac.

Slow-Drying Colors.—In the use of certain color pigments it is well to keep in mind that some dry more slowly than others. For instance, the principal slow-drying colors are lampblack, chrome yellow, yellow ochre, chrome green, and the oil soluble aniline colors.

In using slow-drying colors, where only a small quantity is added to a white paint to make light tints, you will experience no difficulty with slow-drying or tacky paint, but where these colors constitute a rather large proportion of the paint mixture it is wise to increase the amount of Japan drier and turpentine in the paint, especially for hot, humid or cold wet weather.

Madder Lake (not alizarine Madder) should not be mixed with Mars yellow, Mars red, Mars violet or golden ochre. This to avoid unfavorable chemical reactions.

Cadmium yellow ought not to be mixed with any of the lead colors, chrome yellow, orange chrome or American vermilion, or with copper colors like Emerald green, verdigris green or malachite green as unfavorable chemical reactions result.

Zinc yellow when exposed to strong light changes to a green hue but after such a change it remains a permanent light green valuable for lemon and greenish yellow tints.

Cerulean blue has a tendency to turn to a greenish hue with age.

Verdigris green must not be mixed with lake colors. It violently attacks them and is quite fugitive in light itself.

Antwerp blue and raw sienna should not be mixed together. The sienna destroys the blue color rather rapidly.