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done. This great transparency enables the color(?) manufacturer to add it in nearly any proportion desired to colored pigments. But it is after all mainly as an adulterant of white lead and zinc white, that it shows up to the best advantage—as an adulterant. It is the nearest substance in weight to white lead, being very heavy, and known as heavy spar in lead mines where it is frequently found. This great density permits the use of a package for the adulterated lead little greater than that used for the strictly pure article. It is said nearly—but not quite. An expert will detect even the slight enlargement of the package necessary to contain a given weight.
b. Some of the colored pigments themselves are adulterated with barytes to an extent and degree incredible to the uninitiated. Some of the stronger ones are frequently met with—especially in the dry state, containing as much as ten or twelve times their own weight of barytes, while in such pigments ground in oil the proportion ranges from 75% to 500% in extreme cases.
The pure food laws, so called, are of doubtful utility in that in most states the percentage of each substance or ingredient in a compound is not stated, but the adulteration is only indicated by the mention of its presence. So one is left to guess at it. In the preceding paragraph 4 b. it is stated that the proportion may be anywhere from 75% to 500%. Seventy-five per cent., nigh as that may sound (1 part color to 3 parts
adulteration) is legitimate for many colors that are very strong and which cover well in the self color, or which are very seldom used for tinting purposes. Chrome green and all the fancy named proprietary greens, by common consent and custom have sanctioned it, are all made on that basis. The pure color used in painting in its self color will cover very little more surface than the commercial, which is adulterated in the proportion stated of 3 to 1. In that it cheapens the cost of the goods, it really becomes a benefit to the consumer, that is when confined to the well known trade custom limits —but unfortunately it is not always done, and in the dry colors especially, the coloring matter contained in some goods is little more than that used in the preparing of colored chalk.
5. To detect the amount of adulteration present is not so difficult as may be supposed it is. There are two very distinct methods of doing this. First, by a chemical analysis (quantitative) which, if properly made, will give a complete tale of the quantity of each ingredient entering into the compound. As most of the readers of this book are not chemists and as the cost of an analysis properly made will usually cost far in excess of the value of the material under examination, it must be waved aside as impracticable to most people.
While without question a chemical analysis is the most satisfactory, and only correct manner of determining adulteration accurately, fortunately there is a way of approximatively fixing the amount of it in any goods that no one need buy adulterated goods without knowing very nearly just what he is paying for; nor has one any need of a knowledge of chemistry in making the test.
6. This test is called the "Scale test." To make the test all the implements required is an accurate pair of scales with weights in grains or grammes. What are known as army surgeon's scales or any of the apothecaries' pocket scales will do. A few sheets of waxed paper. A few pieces of glass, well cleaned, to lay the colors upon. A palette knife to triturate the colors with and some blotting paper to absorb the oil out of colors so that each may have the same consistency. The above or equivalents are all the appliances needed to equip one for testing
7. The testing is made in the following manner: The person wishing to make a test should have a sample which is well known to be genuine to use as a standard to judge of the value of a similar color about to be tested. These standard colors can easily be procured at any color or painter's supply store, by procuring tubes of Windsor and Newton's artist colors in tubes. These are standard colors of known purity and while there may be a number of others as good as they, none will surpass them and they will be found better, while many will be found inferior to them. So that if W. & N.'s are not procurable any other made by a reputable house will be found sufficiently good for the purpose.
Now it stands to reason that if two similar colors ta
be tested are equally pure that an equal weight of each color when triturated with two batches of white lead both also of an equal weight it follows that when the two colors have been mixed each one separately with the lead—that the tint made will be very nearly of the same strength of tone if both are equally pure, but that if one has been adulterated then it must lack in coloring matter to about the same quantity or percentage as had been added of adulteration to the pure color in the first place.
Thus if one grain or gramme of say-chrome yellow, is carefully placed upon a small square of waxed paper (about 34 inch square) and afterward weighed carefully upon the balances, then placed upon a piece of glass, rubbing the waxed paper over the glass to remove all traces of color from it; then triturated with say 50 grains or grammes of white lead, also placed on waxed paper and carefully weighed, the tint resulting from the triturating should be spread out on the glass, bringing it quite to one edge of it on one side, so as to permit of an easy inspection of each sample when placed side and side together; then afterward doing the same with the other color in each case in like manner, that if there be no adulteration that there will be but very little difference in the tints made.
If the color examined has been adulterated, the tint it will make with white lead will be much weakened as stated before. Now to determine in a sufficiently accurate manner what the proportion of adulterant has been added to it—all that will be necessary will be to add more white lead to the tint made by the stronger color until it is reduced to the strength of the tint made by the weaker color. The tint made by the addition of more white lead should be reweighed.
Thus if one grain of color and 50 grains of white lead produced a tint that is fully equalled by one grain of another color and 250 grains of white lead, it must be that the color which is the weakest has been adulterated with four times its own weight of some kind of an adulterant which has lessened the proportion of coloring matter to the same proportion that the adulterant contained in it bears to the pure.
This test is especially valuable for all chemically made colors having well known formulas. It is useful, however, to determine the relative value of most all the earth colors also with the exception of some very few transparent ones whose chief value consist in this very transparency and their brilliancy of tone. In the latter case the mere strength test is of little value. Under the subject head of colors by referring to paragraphs 61 to 74, fuller information is given regarding their value and really substitution takes the place of adulteration for such.
8. To test adulteration in white lead made by the Dutch process or the hyd.-carb. of lead, a very simple test is made use of to detect such. Place a small bit of the lead to be tested upon a sliver of pine wood, light a match, bring the flame from it in contact with the lead