EXPERIMENTS.
To adopt and practise in earnest any new system without sufficient trials and proofs of its merit, may be called going wilfully astray.—To avoid deceiving myself in the new system before us, I, after having been convinced of its advantageous practicability, set about to ascertain the other great point, the stability of the colours; for this end, and to know more exactly how much every colour would vary from its original hue in a certain space of time, as well in regard to the same system as in opposition to oil-colours, I proceeded as follows.
Experiment the first and principal, 1757.
I had all the colours used in oil painting, mentioned in the foregoing list, carefully ground with water, at Mr. Sandys’s, colour-merchant, and from those colours I composed ninety various and sensibly differing tints, for flesh, drapery and landscape; of each tint I had a quantity of a two ounce gallipot full, tempered with water; so I left them well screened from dust till they were become dry again; then I divided each mass of tint in four equal parts; two of each I set by for the comparative use, the other two parts of each I employed in the following manner.
One part of each I tempered again with water, and painted with it over a space of cloth of six inches wide and two inches high, the tints close to each other, in the manner of copper-plate, [page 58], and the cloth waxed as directed Art. IV. [page 26]. The same I did with the entire and unmixed colours.
The other parts of each tint I tempered with the finest nut-oil according to custom, and painted-over with them such another space of six inches by two, as the former, upon oil-cloth. The same I did with the entire colours, and set them by to dry; when dry, I brought the encaustic tints near the fire, and by melting the wax fixed them.
My tints thus ready, I cut each piece of cloth, encaustic and oil-tints, in five equal parts, and disposed of a piece of each in the following manner.
1. One piece of each I exposed in the open air to all the injuries of sun, dew, wind and rain.
2. One piece of each I nailed to a wall in a damp cellar-like room.
3. One piece of each I nailed to the ceiling of a kitchen and near the chimney, where all the year round a fire was kept.
4. One piece of each I nailed to the side of a room I usually inhabited.
5. One piece of each I put between several quires of paper, and confined them in a close drawer deprived of air.
Thus I left them, till the latter end of October, 1759, (the space of twenty-seven months) when I gathered them. Then I took the two parts of tints I had set by and preserved, and tempering the one with water, and the other with oil, painted the first upon a fresh piece of waxed cloth and fixed them, the other tempered with oil, I painted upon a fresh piece of oil-cloth, and after having washed the old tints, on comparing the new and old colours together found as follows.
The old encaustic entire colours and tints of number 1. seemed to have suffered a considerable change in opposition to the new ones, but compared to their old fellows in oil they looked bright.
I washed them both with common water, and a brush, the encaustic tints recovered a little; oil-tints not.
I brought the encaustic to the fire, and most tints recovered their original hue, and were equal to the new ones, pinks, yellow-orpiment, lake, terra di Siena, and verditer excepted; the first was partly gone, what remained was dull; the second was grown whiter; lake grown lighter, but had not suffered in beauty of colour; terra di Siena crude, grown rough and dirty; verditer, a little dull.
No. 3. seemed to have suffered by the smoke; but after washing it with a stout brush, and soap and water, it recovered its original hue, pinks, yellow-orpiment, smalt and verditer excepted; the first was sensibly decayed; the second grown darker, inclining towards red-orpiment; the third grown dull, but mixed with Prussian blue it was as bright as the new; verditer grown dark and dull.
No. 2, 4, 5. were just as the new ones, there was no difference.
Oil colours did not stand the test so well; their general appearance in opposition to old and new encaustic,—was:
No. 1. weak, dull and dim, some entirely gone.
No. 2. freckled, of all sorts of hues, not to be washed off.
No. 3. darker, some dull, others dirty, some entirely gone.
No. 4. considerably yellower, and less bright.
No. 5. yellow-spotted, as if varnished with gall.
The foregoing tints were all fixed with virgin-wax, which I thought the best; but having at the same time and with the same colours painted upon cloth waxed with common yellow bees-wax, I found that the latter in the open air preserved the colours rather better.
Experiment the second.
I washed the foregoing tints with a strong lixivium of pot-ash, vinegar, spirit of wine, a solution of sea salt, and aqua fortis.
By this operation the oil-colours were entirely destroyed, the encaustic suffered nothing, only smalt grew darker; but after scraping it and bringing it again to the fire, it recovered its tone.
I have still a little scrap of a picture, a landscape, by me, which has undergone all the abovementioned trials and more, for I took it from the frame and folded it in four, put it upon the frame again, and brought to the fire and the folds disappeared,—the colours are as fresh as if painted but yesterday. On examining it close one may perceive it suffered violence, but at a yard’s distance no marks appear.
Experiment on oil-colours.
Having perceived that oil-colours, painted upon a waxed ground always appeared brighter upon an oil-cloth; I, to come at the knowledge of the cause of this effect, contrived various experiments, but without success; at last I made microscopical observations, and found that oil-colours painted upon an oil-cloth undergo a great fermentation, five or six hours after being laid on, and continue so till they are dry. Then they begin to overcast, and by degrees cover the surface with a yellowish, grey substance, not to be washed or rubbed off but with a knife.
Among the very same colours painted upon an encaustic ground I could perceive no such fermentation, or overcasting.—From this we may conjecture that the priming, or ground we work upon is more the cause of the colours changing than the colours themselves, very likely owing to the desecated saline particles of the oil, which are dissolved by and mix with the new oil and colours; or to the superabundant quantity of salts contained in the ground or priming, which is generally composed of the coarsest oil and colours, and frequently half chalk.
Though this latter experiment has nothing to do with encaustic, it will find its application and owner.
To prove the stability of encaustic colours, I have mentioned but two experiments; they are sufficient; from them we may draw the following