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