It is usual with many to use the water pure; but a few drops of potash liquid mixed with it will be found to produce better effect, the marble being rendered more distinct.
GLAIRE.
Put spirits of wine in a proportion of two drops to the whites of twelve eggs, and beat the whole well together till perfectly clear.
PREPARATIONS OF THE COLOURS.
The preparations used by different binders vary much, as will be seen by the recipes given for the same colours, which we judge necessary to put on record, that nothing connected with the subject should be omitted, premising that each colour may be depended upon for producing the most satisfactory results. It may be proper also to observe that the whole of the woods and other ingredients used should be previously powdered or reduced to small pieces, the colours being thereby much better extracted.
BLACK.
1. Dissolve half a pound of green copperas in two quarts of water. The oxide contained in the sulphate of iron will combine with the tanning of the leather, and produce a good black.
2. Boil in a cast-iron pot a quart of vinegar, with a quantity of rusty nails, or steel-filings, till reduced one-third, taking off the scum as it rises to the top. This liquid improves by age. To keep up the quantity, boil with more vinegar.
3. A cheaper liquid may be produced by boiling two pints of beer and two pints of water with two pounds of old iron and a pint of vinegar, scumming as before, and bottling for use.
BROWN.