The preparation of oil varnishes requires the application of considerable heat, and owing to this and the highly inflammable nature of the materials, the process is attended with considerable risk of setting the building on fire. The process should, therefore, always be conducted in detatched buildings constructed expressly for the purpose. Owing partly to the necessity for this precaution, and the circumstance that oil varnishes are greatly improved by being kept in leaden cisterns for some months before they are used, the preparation of oil varnish is carried on almost exclusively as a separate manufacture, the details of which are greatly varied, and are mostly kept secret.

The copper pot employed to make the varnish is called a gum-pot, and measures about two feet nine inches in height, and nine and a half inches diameter externally. The bottom is hammered out of a single piece of copper, and fashioned like a hat without a brim; it is about nine inches deep, and three-eights of an inch in thickness. The upper part of the pot is formed as a cylinder, of sheet copper, about two feet two inches in height, and of sufficient diameter to slip about two inches over the upper edge of the bottom piece, to which it is firmly rivited. A wide flange of copper, to support the pot, is also fixed just beneath the lower edge of the cylinder, and a strong iron hoop is fixed a little above the line of the rivets, to serve for the attachment of the horizontal handle, which is made as a nearly straight rod, one inch square, flattened at the end, and two feet eight inches long.

The stirrer is a copper rod about three-quarters of an inch diameter, and three feet six inches long, flattened at the one end to one and a half inch in breadth for about eight inches in length, and fitted at the opposite end with a short wooden handle.

The ladle, which should contain about two quarts, is also of copper beaten out of the solid, and riveted to a handle of the same metal, three feet six inches long, and fitted with a wooden handle like the stirrer.

The copper jack, for pouring hot oil into the gum-pot, is made in the form of a pitcher, with a large handle and a wide spout; it contains two gallons. The brass or copper sieve, for straining the varnish, is about nine inches diameter, and contains sixty meshes to the inch. The copper funnel, for straining the boiling varnish, i- large enough to receive the sieve, and should be well made with lapped seams, as solder would be melted with the heat.

The tin pouring-pot, to hold three gallons, is formed exactly like a garden watering-pot, only smaller at the spout, and without any rose This is never to be used for any purpose except pouring oil of turpentine into the varnish.

A small broom, termed a "swish," used for washing out the gum-pot every time after use, is made from cuttings of cane tied to a small handle like a hearth-broom; the head is five inches long, and five inches round. This should be washed in turpentine, and kept very clean.

A three-footed iron trevet, with a circular top, is employed to support the gum-pot. The feet of the trevet are about sixteen inches in height, and spread wider at the bottom than the top, which is made of such a size that the pot will fit easily into it, the flange resting on the top.

An ash-bed should be prepared near the fire, upon which to place the gum-pot when the varnish is ready for mixing, or the heat is becoming too great. This is prepared by sifting some dry ashes through a fine sieve, to make a smooth layer about one and a half inch thick, and a little larger than the bottom of the gum-pot.

Place the trevet in a hollow in a field, yard, garden, or outhouse, where there can be no danger from fire; raise a temporary fireplace round the trevet with loose bricks, after the same manner that plumbers make their furnaces; then make up a good fire with either coke, coal, or wood charcoal, which is far preferable; let the fire burn to a good strong heat, set on the gum-pot with three pounds of gum copal; observe that if the fire surround the gum-pot any higher inside than the gum, it is in great danger of taking fire. As soon as the gum begins to fuse and steam, put in the copper stirrer, and keep cutting, dividing, and stirring the gum to assist its fusion; and if it feels lumpy and not fluid, and rises to the middle of the pot, lift it from the fire and set it on the ash-bed, and keep stirring until it goes down (in the mean time let the fire be kept briskly up); then set on the gum-pot again, and keep stirring until the gum appears fluid like oil, which is to be known by lifting up the stirrer so far as to see the blade. Observe, that if the gum does not appear quite fluid as oil, carry it to the ash-bed whenever it rises to the middle of the pot, and stir it down again (keep up a brisk fire), put on the pot and keep stirring until the gum rises above the blade of the stirrer; call out to the assistant, "be ready!" He is then, with both hands, to lay hold of the copper-pouring jack, charged with (one gallon) clarified oil, and lean the spout about one inch and a half oyer the edge of the gum-pot. Let him keep himself firm, steady, and collected, and not flinch, spill, or pour the oil, which would perhaps set all on fire-Obserye, when the gum rises within five inches of the pot-mouth, call out, "pour!" The assistant is then to pour in the oil very slowly until towards the last, the maker stirring during the pouring.

If the fire at this time is strong and regular, in about eight or ten minutes the gum and oil will concentrate and become quite clear; this is to be tested by taking a piece of broken window-glass in the left hand, and with the right lifting up the stirrer and dropping a portion of the varnish on it; if it appears clear and transparent, the oil and gum are become concentrated or joined together. It is now to be farther boiled until it will string between the finger and thumb; this is known by once every minute dropping a portion on the glass and taking a little between the forefinger and thumb. If it is boiled enough it will stick strong, and string out into fine filaments, like bird-lime; but when not boiled enough, it is soft, thick, and greasy without being stringy. The moment it is boiled enough, carry it from the fire to the ash-bed, where let it remain from fifteen to twenty minutes, or until it is cold enough to be mixed; have at hand a sufficient quantity of oil of turpentine to fill the pouring-pot (two gallons); begin and pour out with a small stream, gradually increasing it, and if the varnish rises rapidly in the pot, keep stirring it constantly at the surface with the stirrer to break the bubbles, taking care not to let the stirrer touch the bottom of the pot, for if it should, the oil of turpentine would be in part converted into vapor, and the varnish would run oyer the pot in a moment; therefore, during the mixing, keep constantly stirring as well as pouring in at the same time. Have also a copper ladle at hand, and if it should so far rise as to be unmanageable, let the assistant take the ladle and cool it down with it, lifting up one ladleful after another, and let ting it fall into the pot. As soon as the varnish is mixed, put the varnish sieve in the copper funnel placed in the carrying tin, and strain the varnish immediately; empty it into open-mouthed jars, tins, or cisterns, there let it remain and settle, and the longer it remains the better it will become. Recollect when it is taken out, not to disturb or raise up the bottoms.

Instead of the ash-bed, a circle of loose bricks four courses high may be erected to support the gum-pot. The bricks are to be laid so that when the gum-pot is set within, it will rest securely by its flange with the bottom about six inches from the ground. Upon this brick-stand set the pot every time there is occasion to carry it from the fire. Near the stand an iron trevet may be placed, upon which to turn the gum-pot every time after it is washed out, as, by so doing, it will always be kept clean, and cool gradually, for by cooling rapidly copper oxidizes very quickly. Near the trevet have the swish broom and also a large wide tin jack or other vessel to receive the washings. Have also at hand a copper ladle, and a tin bottle with turpentine, for washing with when wanted.

The moment the maker has emptied the gum-pot, throw into it half a gallon of turpentine, and with the swish immediately wash it from top to bottom, and instantly empty it into the tin jack. Afterwards, with a large piece of woolen rag dipped in pumice powder, wash and polish every part of the inside of the pot, performing the same operation on the ladle and stirrer; rinse them with the turpentine washings, and at last rinse them altogether with clean turpentine, which also put to the washings, wipe dry, with a clean soft rag, the pot, ladle, stirrer, and funnel, and lay the sieve so as to be completely covered with turpentine, which will always keep it from gumming up Eight pounds of copal takes in general from sixteen to twenty minutes in fusing, from the beginning till it gets clear like oil; but the time depends very much on the heat of the fire and the attention of the operator. During the first twelve minutes while the gum is fusing the assistant must look to the oil, which is to be heated at a separate fire in a copper pot, large enough to contain double the quantity required. The oil should be brought to a smart simmer, for it ought neither to be too hot nor too cold, but in appearance beginning to boil, which the assistant is strictly to observe; and. when ready, call to the maker; then immediately each take hold of one handle of the boiling-pot and carry it to the ash-bed, the maker instantly returning to the gum-pot, while the assistant ladles the hot oil into the copper- pouring jack, bringing it and placing it at the back of the gum-pot until wanted.

A thick piece of old carpet, free from holes, should be kept at hand in case the gum-pot should take fire; should thi6 happen, let the assistant throw the piece of carpet quickly oyer the blazing pot, holding it down all round the edges; and in a few minutes-the fire will be smothered.

After the oil has been mixed with the gum, a brisk strong fire should be kept up, until a scum or froth rises and covers all the surface of the contents, when it will begin to rise rapidly. Observe when it rises about two-thirds the height of the pot, carry it from the fire, and set it on the ash-bed, or brick-stand, stir it down again; and if driers are to be added, scatter in a few by a little at a time; keep stirring, and if the frothy head goes down, put the pot on the fire, and introduce gradually the remainder of the driers, always carrying the pot to the ash-bed when the froth rises about two-thirds the height of the pot. In general, if the fire be good, all the time a pot requires to boil from the time of the oil being poured in, is about three and a half or four hours; but time is no criterion for a beginner to judge by, as it may vary a according to the weather, the quality of the ingredients, or the heat of the fire; therefore, about the third hour of boiling, try it on a bit of glass, and keep boiling it until it feels strong and stringy between the fingers, as before mentioned.