The normal strength of size can be discerned without araometer or other recommended apparatus. My opinion is that 2/5 of an ounce of good carrageen moss to a quart of water are sufficient, as carrageen excels all other glutinous bodies by the quantity of mucilage contained in it. To test the correct strength of the size pour some of it into a flat vessel, as a plate or dish, and throw a drop of color upon it; if the color does not spread out, but rather sinks down a drop of ox-gall must be added. Renew the test and so on until the color spreads out to about 2 inches, then take the stylus and draw the color into lines as in producing comb-edges. If the size be too thick the color will be drawn along by the stylus and cannot be cut clean through. On the other hand if the size be too thin it can be seen immediately in its quivering and the running of the color, which cannot be drawn into straight lines. In the former case some clean water must be added to the size, in the latter case which, if the size be well boiled, seldom occurs, thick size must be added by boiling more. The real consistency of the size is so easily learned in practice that a mere feeling with the fingers will be sufficient. The preparation of the colors is carried on separately on a small part of the size, so that the whole quantity is not rendered useless. If the colors are rightly prepared in proportion to their expansibilities in relation to each other, the new size is to be poured into the trough and the marbling may begin. The mistake which is commonly made in marbling is, that too little attention is paid to the size and color. Frequently the size is soiled and the colors are spoiled by adding too much gall before an edge is produced. For this there are generally three causes, either the size is too fresh, too thick or the colors have been prepared on the same size by which the edges are to be produced. Each size which is boiled should only be taken into use after perfect cooling and after several hours have elapsed, since in a warm state it would not permit the colors to expand even by adding a large quantity of gall. Only after the expiration of ten or twelve hours after boiling will it have the correct quantity of mucilage and then only the size possesses its full value. This time having elapsed, the size is filtered through a cloth and is then ready for use. A size when too thick, allows the colors to expand only with great difficulty and demands a three fold larger quantity of gall than when it possesses its normal consistency. It is very difficult to remove from a too consistent size the remnants of colors. They always unite with the size and in this way the size not only becomes soiled but it is impregnated with a large quantity of gall. As I said before, the colors should always be prepared on a separate size which can be poured into a flat vessel as it is nearly impossible to prevent several drops of color sinking to the bottom.