220 
PAINTING. 
in the Aldobrandine picture, are all produced by mix¬ 
tures of ochres with black. Thofe in the Aldobrandine 
picture yield oxyd of iron to muriatic acid; but the 
darker fiiades were not touched by that acid. 
Of the Whites of the Ancients. —The white colours in 
the Aldobrandine pifture are foluble in acids with effer- 
vefcence. and have the charafters of carbonate of lime. 
The principal white in the vafe of mixed colours appears 
to be a very fine chalk. There is another white, with a 
tint of cream-colour, which is a fine aluminous clay. 
The whites from the baths of Titus, and thofe from other 
ruins, are all of the fame kind. 
Cerufe was not met with amongd'the ancient colours, 
though we know from Theophraftus, Vitruvius, and 
Pliny, that it w'as a common colour: and Vitruvius de- 
fcribes it as made by the adlion of lead upon vinegar. 
-Of the Manner in which the Ancients applied their Colours. 
It appears from Vitruvius, that the colours ufed in 
frefco-painting were applied moift to the furface of a 
itucco formed of powdered marble cemented by lime ; lie 
dates that the wall or ceiling had three diftinft coatings 
of ducco made of this material, of which the firfl con¬ 
tained coarfe powder of marble, the fecond the finer pow¬ 
der, and the third the fined powder of all ; and that after 
this the wall was polifhed before the colour was applied. 
The ftuccos that remain in the ruins of the baths of 
Titus and Livia are of this kind, and fo is the ground of 
the Aldobrandine pifture; they are beautifully white, 
and almod as hard as marble, and the granular marble of 
different degrees of iinenefs may be didinguifhed in them. 
This circumdance, indeed, offers a teft of the antiquity of 
ruins at Rome. In the houfes-thathave beenbuiitin the 
middle and latter ages, decompofing lava has been mixed 
with the calcareous cement, in (lead of granular marble ; 
and the ftuccos of thefe houfes are grey or brown, and 
very coarfe in their texture. 
Pliny fays, that purple, orpiment, cerufe, the natural 
azure, indigo, and the meline white, were injured by ap¬ 
plication to wet ducco; which is eafily explained in the 
cafe of orpiment, carbonate of copper, cerufe, and indigo, 
from their chemical compofifion. 
Vitruvius dates, that in frefco-painting vermilion 
changed, if expofed to light; and he recommends the en- 
caufiic procefs for fixing the colour under this circurh- 
itance, namely, laying over it a coat of punic wax, and 
liquifying the wax fo as to make avarnifh for the colour. 
(See p. 215.) Pliny defcribes this procefs as applied in 
painting drips; and we know from his authority, that fe- 
veral pictures of the great Greek maders were painted in 
encaudic, and that the diderent colours were laid on 
mixed with wax. “ I have examined feveral pieces of 
the painted duccos found in the diderent ruins, and like- 
wife the Aldobrandine picture, with a view of afcertain- 
xng if any application had been made to fix the colour; 
but neither by the ted of alcohol, nor by heat, nor by 
the action of water, could I detect the prefence of any 
wax-varnidi, or animal or vegetable gluten. 
“ The pot of colours to which I have already referred, 
found at Pompeii, was blackened by fmoke, as if it had 
been recently on a fire of wood. I thought that this 
might be owing to fome procefs for didolving gluten or 
varnidi in the preparation of the colour; but I could de¬ 
left no fubdance of this kind mixed with the colouring- 
matter. Pliny dates, that gluten (our glue) was ufed in 
painting with blacks ; and this fpecific mention of its ap¬ 
plication would induce the belief that it was not em¬ 
ployed with other colours, which adhered without diffi¬ 
culty to, and u'ere imbibed by, a furface fo polifhed and 
well prepared as the Roman ducCo; and the lightnefs of 
carbonaceous matter alone probably rendered this appli¬ 
cation neceffary. 
General Obfcrvations by Sir II. Davy. —It appears from 
the fafts that have been dated, and the authorities quoted, 
that the Greet and Roman painters had almod all the 
fame colours as thofe employed by the great Italian maf- 
ters, at the period of the revival of the arts in Italy. 
They had indeed the advantage over them in two colours ; 
the Veftorian or Egyptian azure, and the Tyrian or ma¬ 
rine purple. 
The azure, of which the excellence is proved by its du¬ 
ration for feventeen hundred years, may be eafily and 
cheaply made; I find that fifteen parts by weight of car¬ 
bonate of foda, twenty parts of pou’dered opaque dints, 
and three parts'of copper-filings, drongly heated toge¬ 
ther for two hours, gave a fubdance of exaftly the fame 
tint, and of nearly the fame degree of fufibility, and 
which, when powdered, produced a fine deep fky-blue. 
The azures, the red-and-yellow ochres, and the blacks, 
are the colours that feem not to have changed at all in 
the ancient frefco-paintings. The vermilion is darker 
than recently-made Dutch cinnabar; and the red-lead 
is inferior in tint to that fold in the diops. The greens 
in general are dull. 
The principle of the compofition of the Alexandrian 
frit is perfeft; namely, that of embodying the colour in 
a compofition refembling done, fo as to prevent the ef- 
cape of elaftic matter from it, or the decompofing aftion 
of the elements ; this is a fpecies of artificial lapis lazuli, 
the colouring-matter of which is naturally inherent in a 
hard filiceous done. It is probable that other coloured 
frits may be made, and it is worth trying whether the 
beautiful purple given by oxyd of 'gold, cannot be made 
ufefui in painting on a denfely-tinted glafs. Where frits 
can be employed, metallic combinations, which are infa¬ 
llible in water, and which are faturated with oxygen, or 
fome acid matter, it is evident from the proof of a dura¬ 
tion of feventeen centuries, are the bed pigments. In 
the red ochres, the oxyd of iron is fully combined with 
oxygen and carbonic acid ; and thefe colours have not 
changed. The carbonates of copper, which contain an 
oxyd and an acid, have changed very little. Mafficot and 
orpiment were probably the lead permanent amongd the 
ancient mineral colours. 
Of the colours the difeovery of which is owing to the 
improvements in modern chemidry, the patent yellow is 
much more durable than any'ancient yellow of the fame 
brilliancy ; and chromate of lead, an infoluble compound 
of a metallic acid with a metallic oxyd, is a much more 
beautiful yellow than any poffeffed by the’ancients; and, 
there is every reafon to believe, is quite unalterable. 
Scheele’s green (the affenite of copper) and the infa¬ 
llible muriatic combination of copper, will probably be 
found more unalterable than the ancient greens; and the 
fulphate of barytes offers a white fuperior to any poffeffed 
by the Greeks and Romans. 
I have tried the efteft of light and air upon fome of the 
colours formed by the .new fubdance iodine. Its combi¬ 
nation with mercury offers a good red; but it is, I think, 
lefs beautiful than vermilion, and it appears to change 
more by the aftion of light. Its compound with lead 
gives a beautiful yellow, little inferior to the chromate of 
lead; and I poffefs fome of this colour which has been 
expofed to light and air without alteration for feveral 
months. 
In many of the figures and ornaments in the outer 
chambers of the baths of Titus, where only outlines or 
fpots remain, or fhades of ochre, it is probable that vege¬ 
table or animal colours, fuch as indigo and the different 
dyed clays, were ufed. Some excellent pictures have dif¬ 
fered very much in modern times from the fame caufe 
the lakes in the frefcos of the Vatican have lod much of 
the brilliancy which they mud have poffeffed originally. 
The blues in many piftures of Paul Veronefe are become 
muddy. 
Pliny fpeaks of the celebrated Greek painters as em¬ 
ploying only four colours; white, yellow, red, and black ; 
but, as far as Apelles and Nicomachus are concerned, this 
is a midake; and it is not unlikely that Pliny was milled 
by an iinperfeft re.oolleftion of a p.affage in Cicero, who 
defcribes 
