Fuse six pounds of fine-picked very pale transparent amber in the gum-pot, and pour in two gallons of hot clarified oil. Boil it until it strings very strong. Mix with four gallons of turpentine. This will be as fine as body copal, will work very free, and flow well upon any work it is applied to; it dries slowly, but becomes very hard, and is the most durable of all varnishes. It is very excellent to mix in copal varnishes, to give to them a hard and durable quality. Amber varnish is, however, but little used, on account of its expense.

In making all the above varnishes, it should be observed that the more minutely the gum is fused, the greater the quantity and the stronger the produce. The more regular and longer the boiling of the oil and gum together is continued, the more fluid or free the varnish will extend on whatever it is applied. When the mixture of oil and gum is too suddenly brought to string by too strong a heat, the varnish requires more than its just proportion of turpentine to thin it, whereby its oily and gummy quality is reduced, which renders it less durable; neither will it flow so well in laying on. The greater proportion of oil there is used in varnishes, the less they are liable to crack, because the tougher and softer they are. Increase the proportion of gum in varnishes, the thicker the stratum required, and the firmer they will set, and the quicker they will dry.

All body varnishes, or those intended to be polished, should have one and a half pounds of gum to each gallon of varnish when it is strained off and cold. All carriage or wainscot varnishes or those not intended to be polished, should have full one pound of gum to each gallon. But the quantity of gum required to bring it to its proper consistence, depends very much upon the degree of boiling it has undergone; therefore, when the gum and oil have not been strongly boiled, the varnish requires less turpentine to thin it, and when boiled stronger than usual, a larger proportion of turpentine is required; if the mixing of the varnish with the turpentine is commenced too soon, and the pot is not sufficiently cool, there may be considerable loss by evaporation.

Copal varnishes should be made at least three months before they are required for use, and the longer they are kept the better they become; but when it is necessary to use the varnishes before they are of sufficient age, they should be left thicker than usual.