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Researching the Fortress of Louisbourg National Historic Site of Canada
  Recherche sur la Forteresse-de-Louisbourg Lieu historique national du Canada




A. Storm

May 1982

(Fortress of Louisbourg
Report H G 05)

Chapter II


Resin finishes as used in the eighteenth century could be defined as solutions or dispersions of resin in a liquid solvent that, when spread in a thin layer on the surface of an object, dried either by the evaporation, or polymerization, of the solvent, or both. They formed a hard, transparent coating that imparted a gloss and lustre to a surface and protected it from the weather. The popularity of varnishes, as they were commonly called, was more easily attributed to their decorative rather than their protective qualities. Varnishes were the only finishing materials available in the eighteenth century that could form solid yet transparent films capable of accentuating the natural beauty of wood.

Basically, three different types of varnishes were commonly used. Each kind was named for the solvent that was employed to dissolve the resin. The first class, called SPIRIT VARNISHES, were in use by the seventeenth century. [1] These varnishes were made by dissolving resin in alcohol or some other highly volatile fluid. Similarly, ESSENTIAL OIL VARNISHES, the second class, were made by dissolving resin in an essential oil. Turpentine was about the only solvent used for these varnishes. Although it cannot be determined just when they were brought into use, it is safe to assume that it was well before the mid eighteenth century. The last class, FIXED OIL VARNISHES, employed since the twelfth century, consisted of a resin dissolved in a drying oil. [2] The most commonly used solvent for these varnishes was linseed oil.

Varnish-making was an empirical craft, and the study of eighteenth century varnishes is hampered by an abundance of unrelated formulas. Each craftsman developed his own favorite recipes. Many of these formulas were remarkable because they often included useless, if not harmful, ingredients. To study varnishes, then, one can only attempt to draw together the basic formulas and procedures employed in the making of these finishes.

The varnishers' craft was not particularly dangerous to his health, but the one occupational hazard, which he had to guard against constantly, was fire. All the ingredients that were used to make varnishes were flammable, and many processes in manufacturing a varnish called for the direct application of heat to those materials. Fire was quite a common occurrence, it seems, and the varnish maker was constantly reminded to place his work shop far enough away from other buildings so that they would not be endangered "in the event of fire upon the premises." Copal and amber were probably the worst offenders because they had to be melted before they would dissolve in a solvent. When melting these resins, it was advisable to keep a wet blanket nearby to smother a fire should anything ignite.

Varnishing Tools and Processes

Very little in the way of tools and apparatus was required to make varnishes. To manufacture spirit and essential oil varnishes, for example, the basic utensil needed was a glass or tin vessel in which the resins could be dissolved in their proper solvents. The first step in making any varnish usually consisted of grinding the resin into a coarse powder. Small particles of resin were dissolved more easily and quickly. The mixture of solvent and resin was often heated in a water bath to accelerate the action of the solvent. When heated, the small resin particles tended to agglomerate or stick together. This could be prevented, however, to a large extent, by mixing in powdered glass with the resin. Then, as long as the ingredients were stirred while being heated, the glass particles served to agitate the resin and keep it from forming lumps. Once the varnish was made, it could be filtered through cotton, and then it was ready for use.

The first step in varnishing an object was to make sure the surface to be varnished was clean. If a work were being revarnished, it had to be cleaned of dirt and grease with water in which a small quantity of lime or soda had been mixed. Next, if the article were made of wood, all cracks, knots, or defects were filled with putty tinted with pigment to match the color of the wood. Occasionally the surface was given a final sanding by rubbing it down with dried rushes.

Varnish was usually applied with a brush, although it could also be rubbed on with a soft cloth. The brushes, like those for painting, were made of the best quality of hog bristle. They had to be stronger than paint brushes, however, since varnishes pulled more than paints and could tug the bristles out of a paint brush. Round brushes were used.

Varnishes could not be applied, generally, to a cold object, or where cold air currents could reach the fresh varnish. A temperature of above seventy degrees Fahrenheit was "preferred for the varnishing room." If the temperature of the environment dropped below this level, it had a very detrimental effect on the finish:

Not only should the room be sufficiently heated, but all currents of cold air must be avoided; as cold draughts from the interstices of the door or window, if suffered to pass over the recently varnished surface, are quite sufficient to dull the varnish where-ever they extend. [3]

For the most part, four to ten coats of varnish were usually brushed on an object, sometimes more. Each layer was allowed to dry thoroughly before the next was put on, and in the better sort of work each layer was rubbed or polished before it was covered over. After the requisite number of coats had been applied, the varnish film was often polished with pumice powder and tripoli. Pumice powder, made by grinding up a glassy rock of volcanic origin, gave varnish a rough polish. The powder was rather coarse, but when mixed with water and rubbed over the work with a woolen cloth, it served to remove all brush marks and other surface irregularities. Tripoli, a naturally occurring, gritty, ochre-like material, was employed to give the varnish its final polish. It was rubbed on with either a wet or an oiled cloth. The polished surface was then buffed with starch or flour.[4]

Spirit Varnish

Spirit varnishes were made by dissolving a resin, or a mixture of resins, in a highly volatile solvent such as alcohol. When brushed on a surface, the solvent evaporated completely leaving nothing but the resin behind. Spirit varnishes had the advantage of drying rapidly, but they often dried to a brittle, easily cracked finish. If a small quantity of turpentine were added to the varnish, however, it made the protective film more elastic and less liable to fracture. Usually the resins were dissolved simply by allowing the solvent to act upon them. Solution could be hastened by heating the mixture, but the application of heat was liable to darken the varnish. Moreover, it was dangerous to heat the ingredients of a spirit varnish because all the solvents employed were highly flammable.

Many resins were soluble in alcohol and could be used to make spirit varnishes. The most important were: shellac, dammar, mastic, sandarac, Venice turpentine, elemi, and copal. Alcohol was commonly used as a solvent in the manufacture of these varnishes because it seems to have worked better than anything else available, and it was readily available and inexpensive. To dissolve the resin properly, the alcohol had to be highly concentrated. One interesting method of checking the strength of alcohol was to:

pour some into a cup upon gunpowder, and then to set fire to it. If the spirit (alcohol) be sufficiently strong after burning down to the gunpowder, it will inflame (ignite); but if too much water had been mixed with it, that would not take place, as, after the spirit was consumed, there would still be water enough left to keep the gunpowder wet. [5]

Spirit varnishes were particularly important because they were the only variety of varnish that could be made without any color. These colorless finishes had the disadvantage of being soft and easily scratched, but they could be used to cover a white paint without discoloring it. No other varnish could do this. The most important ingredients employed in the making of white or colorless varnishes were sandarac and mastic dissolved in alcohol.

ESSENTIAL OIL VARNISHES were made by dissolving a resin, or a mixture of resins, in turpentine. Like spirit varnishes, they dried by the evaporation of the solvent. For the most part, the solvent evaporated off, leaving the resin behind, but, unlike alcohol, the turpentine probably did not leave the film completely. It seems that a small portion of turpentine remained behind to become an integral part of the varnish. Essential oil varnishes had more body than spirit varnishes. They also were "more pliant, stronger," and less "liable to scale" than the latter. Almost all the resins would dissolve in turpentine, but the ones employed most often for making essential oil varnishes were: copal, dammar, kauri, anime, amber, and Venice turpentine. The best varnishes were made with copay. Copal was readily dissolved in turpentine, if the solution were assisted by the action of camphor or ammonia water, and it made a bright, durable varnish.

Fixed Oil Varnish

Fixed oil varnish was made by dissolving a resin, or resins, in a drying oil. Varnishes of this type were more durable than any of the others, but they had the disadvantage of drying only very slowly. The drying process, however, was accelerated if the oil were first treated with a drier, such as litharge. Oil solvents, unlike the solvents employed a spirit and essential oil varnishes, did not evaporate after the varnish was applied. Instead, they remained in the film, polymerized around the resin particles, and actually helped make a much stronger and tougher varnish. Once the varnishes were made, they often had to be thinned with turpentine to bring them to the proper consistency. Otherwise they were too thick to brush on. Used in this way, turpentine was considered to be a thinner rather than a solvent.

Linseed oil was the favored solvent for fixed oil varnishes, probably because it was readily available and comparatively inexpensive. Poppy seed and nut oil were lighter in color and worked well, but they were most likely reserved for the better types of varnish as they certainly cost more. Many resins, such as anime and Venice turpentine, could be used to make fixed oil varnishes, but amber and copal were employed more often than any of the others. Copal had less color than amber while the latter was more durable. They were usually blended together to make light colored yet extremely tough varnishes.

As previously mentioned, copal and amber both had to be run before they could be dissolved in oil. Once they were partially depolymerized by being heated above their melting point for a short period of time, they were soluble in oil. The run resin was kept melted, or remelted if it had been allowed to solidify, and then hot linseed oil was slowly added to it. Once the ingredients were completely intermingled, the varnish could be thinned to the proper consistency with turpentine and filtered by pouring it through cloth. It was then ready for use. An eighteenth century source describes varnish as:

"a thick, viscous shining Liquor, used by painters, Gilders, and various other artificers to give a gloss and lustre to their works; Us also to defend them from the weather, dust, etc. [6]

WHITE VARNISH - AMBER VARNISH - Take white rosin four drams, melt it over the fire in a clean glazed pipkin, then put into it two ounces of the whitest amber you can get (finely powdered) this is to be put in by a little and a little, gradually, keeping it stirring all the while with a small stick, over a gentle fire, till it dissolves, pouring in now and then a little oil of Turpentine, as you find it growing stiff; and continue to do so till all your amber is melted.

But great care must be taken not to set the house on fire, for the very vapours of the Oil of Turpentine will take fire by heat only; but if it shall happen so to do, immediately put a flat board or wet blanket over the fiery pot, and by keeping the air from it, you will put it out, or suffocate it.

Therefore, it will be best to melt the rosin in a glass of Cylindric figure in a bed of hot sand, after the glass has been well annealed or warmed by degrees in the sand, under which you must keep a gentle fire.

When the varnish has been thus made, pour it into a coarse linen bag, and press it between two hot boards of Oak or flat plates of Iron, after which it may be used with any colors in painting, and also for varnishing them over when painted. [7]

THE WHITE VARNISH - Take Gum Sandarach of the clearest and whitest sort, eight ounces, gum mastick of the clearest sort, half an ounce, of Sarcacolla the whitest, three quarters of an ounce, Venice Turpentine an ounce and a half, benzoin the clearest one quarter of an ounce, white rosin one quarter of an ounce, gum Animæ three quarters of an ounce. Let all these be dissolved, and mixed in the manner following.

Put the Sarcacolla and rosin into a little more spirits than will cover them to dissolve; then add the benzoin, gum animæ and Venice turpentine, into either a glass or glazed earthen vessel, and pour on as much spirits as will cover them an inch; then put the gum mastick into a glass or glazed vessel, and pour strong spirits upon them, covering them also about an inch thick to dissolve them rightly; then put your gum elemi in a distinct vessel as before, and cover it with spirits to dissolve.

For this purpose, you need only break the rosin a little and ponder the gum Animæ Sarcacolla and Benzoin.

Let all stand three or four days to dissolve, shaking the glasses, etc., two or three times a day, and afterwards put them all together into a glazed vessel, stirring them well, and strain the liquor and gums gently; beginning with the gums, through a linen cloth.

Then put it into a bottle, and let it stand a week before you use it, and pour off as much of the clear only, as you think sufficient for present use. [8]

Another approach for the white varnish states that since most colored woods, whether from the Indies or from France, or stained woods, lose their lustre with time, and it is very important to preserve these colors, one can do no better, having finished them with scouring rush and tripoli stone, or with whiting, than to varnish them with white varnish, commonly called Venitian varnish (vernis de Venise). Although the varnish I am speaking of is a little different from the latter, the varnish proper for use on pieces of Cabinetwork is white or, to speak more accurately, colorless. It is composed of one or two pintes of spirit of wine (esprit-de-vin), five onces of sandarac (sandaraque) (the whitest possible), two onces of tears of mastic (mastic en larmes) one once of gum elemi (gomme élémy) and one once of spike oil (huile d'aspic), all melted in the double boiler (bain-marie) without boiling the spirit of wine; and when this varnish is cooled, it is filtered through cotton, so that no dirt of any kind remains in it.

One can apply several coats of this varnish to pieces of Cabinetwork without worrying about the colors being turned darker, by taking care not to put a second coat on before the first is perfectly dry. When two, four or six coats of varnish have thus been applied, and the last coat is perfectly dry, the whole piece is polished with a pad of rolled cloth lists (lisières de crap roulées), or with buff, on which one has put a little tripoli stone moistened with water. Then the piece is washed with clear water and wiped with fine dry cloths.

This method of finishing Cabinetwork is a little more costly and more subject than the others. But for that reason it has the advantage of being the most perfect, for the varnish, by stopping up all the pores in the woods, seizes their color which, no longer being able to evaporate, always remains in the same state, which is a very great advantage, since it is partly in the vivacity of these same colors that the beauty of pieces of Cabinetwork consists, of whatever kind they may be; and this is the only means I know of for giving brilliance to the colors of stained woods. [9]

VARNISH MADE WITH SEED LACCA. Take a pint of strong spirit of wine, put into a glass vessel, and put to it three ounces of Seed Lacca, and let them stand together for two days, shaking them often, then pass it through a jelly bag, or a flannel bag, made like what is called Hypocrate's sleeve, letting the liquor drop into a well glazed vessel, and giving the gums a squeeze every now and then; when the varnish is almost out of the-bag, add more, and press it gently till all is strained, and the dregs remain dry.

Be sure you do not throw the dregs into the fire, for they will endanger setting the house on fire.

Put the varnish up in a bottle, and keep it close stopped, setting it by till all the thick parts are settled to the bottom, which they will do in three or four days, then pour the clear into a fresh bottle, and it will be fit for use.

As for varnish made of Shell-Lacca, it is not of any great service, though so often recommended, for it will not bear the polish.

When you lay on your varnishes, take the following method.

1. If you varnish wood, let your wood be very smooth, close "rained, free from grease, and rubbed with rushes.

2. Lay on your colors as smooth as possible, and if the varnish has any blisters in it, take them off by a polish with rushes.

3. While you are varnishing, keep your work warm, but not too hot.

4. In laying on your varnish, begin in the middle, and stroke the brush to the outside, then to another extreme part, and so on till all be covered; for if you begin at the edges, the brush will leave blots there, and make the work unequal.

5. In fine works use the finest Tripoli in polishing: do not polish it at one time only; but after the first time, let it dry for two or three days, and polish it again for the last time.

6. In the first polishing you must use a good deal of Tripoli; but in the next a very little will serve; when you have done, wash off your Tripoli with a sponge and water; dry the varnish with a dry linen rag, and clear the work, if a white ground, with oil and whiting; or if black, with oil and lamp-black. [10]

A varnish for all sorts of colors: Take of gum ammoniac 1 ounce, of mastic and gum sandarac of each 2 ounces. Reduce them to a fine powder. Put them into a glass vessel and pour a pint of the spirits of wine over them: hang them in the sun or set it by the fire till it is dissolved: then strain it through a clean cloth and keep it in a vial well corked: and then mix your paints with it. [11]

A USEFUL VARNISH - Take drying linseed oil, set it on the fire, and dissolve in it some good rosin, or (which is better, but dearer) gum-lacca; let the quantity be such as may make the oil thick as a balsam. When the rosin or gum is dissolved, you may either work it off it self, or add to it some color, as Verdigrease, for a green; or Amber, for a hair color; or Indigo and white, for a light blue.

This will secure timber-work done over with it, equal to painting with colors in Oil, and is much more easy to obtain; for linseed oil and rosin are more easily melted together, by boiling, than colors can any ways be ground; and being of the consistence of a balsam, works very readily with a brush, and of it self, without the addition of colors; bears a body sufficient to secure all manner of timber work, equal to most oil colors.

In the working of it, there's no great skill required, if you can but use a Painter's brush; only let the matter you lay it on, be thoroughly drenched, that the outside be glazed with it: and if you desire a color on the outside, you need only grind a color with the last varnish you lay on. [12]

To preserve bright iron-work from rust, and other injuries of a corroding air, by an oily varnish.

Take good Venetian, or for want of that the best and clearest common turpentine, dissolve it in Oil of Turpentine, and add to it some linseed oil, made clear by long standing in the hot sun (for some uses the common drying linseed oil may serve;) mix them well together, and with this mixture varnish over any sort of bright iron-work whatsoever.

It is a certain preserver of all such iron-work from rust, let it be what it will, provided it be such as it not brought into common use, for much handling will wear it off, and heat will dissolve it; but for all such bright iron-work that is used about either carpenters or joiners work, that require not much handling; as also arms, etc., that hang up for State, rather than present use, it is an infallible preservative.

When you use this oily varnish, 'tis best to warm it, and then with a brush lay it on as thin as possible; this is best for arms; but for other iron-work, it may be laid on cold; in four or five days after it has been laid on, it will be thoroughly dry.

Note, that such Arms as have been done over with it, may when they come into use be cleansed from it again, by being warmed hot before a fire: or heat will dissolve it, but water will do it no hurt. [13]

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