Cyclopedia of Painting/Varnishes
VARNISHES.
It is not economical for painters to make these for themselves, as they may be purchased both cheaper and in most cases better than they could make them. At the same time it is well to know how to make these important compounds, for it may so occur that the materials may be obtained where the varnish itself could not, or other circumstances may render it desirable that the varnish should be made at home, a few receipts for the purpose are, therefore, given.
Table Varnish. Take of oil of turpentine 1 pound, beeswax 2 ounces, colophony 1 drachm. Dammar resin 1 pound, spirits of turpentine 2 pounds, camphor 200 grains. Allow the mixture to stand for twenty-four hours, and the portion poured off is fit for immediate use.
Furniture Varnishes. Dissolve 11⁄2 pounds of shellac in 1 gallon of naphtha, and it will be ready for use as soon as the dissolution is complete. Dissolve 12 ounces of shellac and 3 ounces of copal, or an equivalent of Copal Varnish, in 1 gallon of naphtha. Dissolve 2 ounces mastic, 11⁄2 pounds shellac, 4 ounces seed lac, 4 ounces sandarach, or 1 gallon of rectified spirits of wine, benzoin, and dragon's blood, tumeric and other coloring matters may be added as required.
Mahogany Varnish. Gum sandarach 2 ounces, shellac 1 ounce, gum benjamin 1⁄2 ounce, Venice turpentine 1 ounce, spirits of wine 1 pint. Color red with dragon's blood, or yellow with saffron, place the vessel containing these ingredients in a warm spot, until the gum has dissolved, then strain for use.
White Furniture Varnish. Dissolve 6 ounces of white wax in 1 pint of oil of turpentine by gentle heat, or white wax 6 parts, petroleum 48. To be applied to the work whilst warm; allowed to cool, and then to be polished by rubbing with a coarse cloth.
Dark Varnish for light wood-work. Shellac 16 parts, gum sandarach 32, gum mastic 8, gum elemi 8, dragon's blood 4, anatto 1, white turpentine 16, alcohol 256. Dilute also with alcohol, if required.
Varnish which resists boiling water. Linseed oil 1½ pounds, amber 1 pound, pulverized litharge 5 ounces, powder white lead 5 ounces, minium 5 ounces. Boil the linseed oil in an untinned copper vessel, and suspend in it the litharge and minium in a small bag, which must not touch the bottom of the vessel. Continue the ebullition until the oil has acquired a deep brown color, then take out the bag, and put in a clove of garlic, this is to be repeated seven or eight times, the boiling being continued. Before amber is added to the oil, it is to be mixed with 2 ounces of linseed oil, and melted over a fire that is well kept up. When the mass is fluid, it is to be poured into the linseed oil, this mixture is to be boiled and stirred continually for two or three minutes. Afterwards, filter the mixture, and preserve it in a bottle well corked up. When this varnish is used the wood must be previously well polished, and covered with a thin coat of soot and spirits of turpentine. When this coat is dry, some of the varnish may be applied with a sponge, taking care that it is equally distributed on every part. This operation is to be repeated four times, being always careful that each coat be well dried before another is put over it. After the last coat of varnish the wood must be dried in an oven, and afterwards polished.
Turpentine Varnish. One pint of spirits of turpentine, 10 ounces clear resin pounded, put it in a tin can on a stove, and let it boil for half an hour. When the resin is dissolved, and the mixture has cooled, it will be ready for use.
White, hard, spirit Varnish. In three pints of rectified spirit dissolve 1 pound of gum sandarach, and add 6 ounces of turpentine. Dissolve 4 ounces gum mastic, 1⁄2 pound gum juniper, in 4 pints rectified spirit, add to the mixture 1 ounce of turpentine. Mastic in tears 2 ounces, sandarach 8 ounces, gum elemi 1 ounce, Chio turpentine 4 ounces, rectified spirit 1 quart.
Mastic Varnish. Immerse 10 ounces of the clearest gum mastic in 1 pint of turpentine, place the vessel containing the mixture in a sand bath until the mastic is all dissolved, then strain it through a fine sieve, and it will be ready for use, if too thick, it may be diluted by the addition of spirits of turpentine.
Copal Varnish. Melt 8 parts of powdered copal gum in an iron pot by slow heat, and 2 parts balsam capivi previously warmed. Then remove from the fire, and add 10 parts spirits of turpentine, also warmed, in order to reduce to the necessary degree of thickness for working.
Gum Copal is made more soluble in spirits of turpentine by melting the powdered crude gum, and allowing it to stand for some time loosely covered. Powdered copal 24 parts, spirits of turpentine 40, camphor 1, 4 ounces copal, 1⁄2 ounce camphor, 3 ounces white drying oil, 2 ounces essential oil of turpentine. Reduce the copal to powder, mix the camphor and drying oil, then heat it on a slow fire, add the turpentine and strain. As other soft resins are sometimes substituted for mastic, so inferior hard resins are sometimes employed in the place of copal, in the composition of varnishes celebrated as copal varnishes. Copal is difficult of solution in turpentine and linseed oils, both of which enter into the composition of the ordinary Copal Varnishes, which are employed by the coach painter and afford the best varnishes used by the house painter and grainer. Combined, however, with linseed oil and oil of turpentine, copal varnish affords a vehicle superior in texture, strength, and durability to mastic and its megilp, though in its application it is a less attractive instrument, and of more difficult management. As copal swells while dissolving, so its solutions and varnishes contract, and consequently crack, in drying, and thence linseed oil is essential to prevent its cracking. The mixture of copal varnish and linseed oil is best effected by the medium of oil of turpentine, and for this purpose heat is sometimes requisite.
Iron-work, Varnish for. Dissolve in about 2 pounds of tar oil, 1⁄2 pound of asphaltum and a like quantity of pounded resin, mix hot in an iron kettle, care being taken to prevent any contact with the flames. When cold the varnish is ready for use. This varnish is for outdoor work and iron-work.
Common work, Varnish for. Place 3 pounds of powdered resin in a tin can, and add 21⁄2 pints of spirits of turpentine, shake well, and allow the mixture to stand for a day or two, shaking it occasionally. Then add 5 quarts of boiled oil, shake the whole, and allow it to stand in a warm room until clear. This clear portion is then to be poured off for use, and may be reduced in consistency by the addition of turpentine. This varnish is intended for protesting surfaces against the effects of exposure to the atmosphere, and has been used with great advantage for coating wood and iron-work.
Defects in Varnishes and their Remedies. In applying oil varnishes to different objects, various defects often make their appearance, these are in many cases very obscure in their origin, although painfully obvious in their effects. The defects may arise through faults in making the varnishes, through defects in the surface of the objects which have been varnished, through faulty methods of application, or through climatic changes. Seeing, therefore, that there are so many factors which produce defects in varnished surfaces, it is no wonder that the causes of such defects are obscure, especially as the varnisher may be of an unobservant character and fail to notice faults at the time the varnish is being applied. Cracks and pinholes: these are often due to climatic changes, especially liable to occur in winter time, when a cold day will follow a hot or warm one. Keeping the object in a warm place for some time will tend to cure this fault, and take care that the varnish cannot get chilled while drying. Peeling, blistering, spots, and crawling are defects which may be traced to a greasy nature of the surface on which the varnish is applied. This may be due to the use of bad pinning, paint, or rubbing the work down with oily rags, or to drops of oil on the surface on which the varnish is applied, and not properly removed in the preparing operations. The remedy consists in preventing the application of oily matters to the surface, and to see that they are thoroughly removed. Sagging: this defect arises from two causes, a very greasy nature of the surface, or from applying the varnish too thickly. The varnisher is tempted to take up too much varnish on his brush, and unless he takes care to spread this well he will leave it too thick, and then sagging or running down may occur. If in the preparatory processes too thick a coat of paint is put on, the varnish may tend to soften this, and then this defect is liable to occur. Sweating and blurring may be due to defects in the manufacture of the varnish, the gums used have not been properly melted and too much of their volatile constituents left in, or the varnish may have been sent out before it was properly matured. Varnishing on a damp surface will also develop these defects. Deadening may be due to faulty preparation of the varnish, but more often it is due to climatic conditions, varnishing in too damp an atmosphere, on damp surfaces, in the presence of deleterious gases and vapors, too porous a subject, too large a proportion of driers used in making it, all of which tend to cause loss of lustre in a varnish, either immediately or after a time. It is difficult under these circumstances to point out a remedy, for one will scarcely know the exact cause in any particular case, and of course it is obvious that the remedy will vary with the cause, and what will do for one case will not do for another. The varnisher should, if he wants to produce a good job, take every precaution to prevent defects arising, for in this case an ounce of prevention is worth a ton of cure. He should see that his varnish is of good quality, that his cans and brushes are in good condition and clean, that the surface he has to varnish is in proper condition, free from grease, dry, and having a smooth surface. He should never attempt a job in wet or damp weather, and he should take care that, after varnishing, his work is not exposed to any bad influences which will retard the drying and hardening of the varnish.