The Sun.
London, England, 1854-09-20 00:00:00

No. 2.

ON THE EMPLOYMENT OF A SOLUTION OF
STARCH IN FRESCO PAINTING, BY MR.
DYCE, R.A.
The Oaks, Norwood, Nov. 21, 1853.
Sir,—ln some observations on fresco addressed by me
to the Commissioners on the Fine Arts in 1846, and
printed by them in the seventh report, I had occasion
to refer to the difficulties experienced by fresco painters
in the use of ultramarine and some other pigments ; and
I suggested that if a solution of starch or of the caseous
element of milk were mixed with the colours, their
adherence to the intonaco might probably be reckoned
upon with certainty.
This was a mere suggestion based on the known fact
that both these subbstances form, with quicklime, a com-
pound which, when it is dry, is insoluble in water.
Since that time, however, I have had ample opportunity
of submitting one of the suggested expedients to the test
of experiment, and the result has been so satisfactory
that I think it desirable to put the commissioners in pos-
session.of the fact, to be recorded for the benefit of future
painters in fresco.

If either of the suggested expedients was likely to
answer, it seemed to me that the use of starch would pre-
sent fewest difficulties of manipulation ; I accordingly
tried it first, and with so successful a result, that I have
thought it useless to attempt the employment of caseine;
' but I may mention that since my suggestion respecting
it was made, a Scottish gentleman has discovered and
obtained a patent for a process of calico-printing by
means of a vehicle prepared from casino and quicklime,
which probably might be employed in fresco painting
for the purposes which I have attained by the use of a
solution of starch. This vehicle is prepared by dissolv-
ing caseine in the liquid ammonia of commerce, and
adding to the solution a certain proportion of quicklime,
the mixture then being diluted with water to any required
consistency ; and the inventor of the process (who entered
into communication with me partly in consequence of
the suggestions I had made in the paper referred to)
thinks that if this vehicle were employed in fresco paint-
ing, and mixed with all the colours, it would not be
necessary to prepare the intonaco day by day, and pro-
vided some expedient were adopted to keep it in a damp
state, that even large pictures might be executed with.
out, or at most with very few, joinings in the plaster.
This, however, I have not tried ; partly from want of
time, but chiefly because the more simple vehicle of a
weak solution of starch, if it would not answer the same
purpose, at least accomplishes the more limited object I
had in view so perfectly as to leave little to desire.
The use of ult-ramarine in a nearly pure state, hitherto
the crux of fresco painters, presents, when the pigment
is combined with a weak solution of starch, no difficulty
whatever, It may be applied with tolerable certainty
of effec,C even when the intonaco has become, as it does
at tb a end of a day, hard and partially crystalised at the
surface.

These conditions, however, must be attended to. In
the first place, the solution must be so weak that when
cold it shall scarcely assume the form of a jelly.
Secondly, it must be used on the day on which it is
prepared. On the second day it undei goes some change
(I do not know what), which has the effect of causing
the colours mixed with it to dry in streaks or blotches.
If the Caine tint, therefore, has to be used on consecutive
days, it must be prepared beforehand with water, and
the vehicle added only to so much of the pigment as may
be required for the day's work.
Thirdly, the effect of the vehicle in fixing the colours
cannot be depended upon with certainty unless the pig-
ments contain a small portion of lime. This may seem
to be an obstacle to the employment of colours in a per-
fectly pure state, but in practice this is of little conse-
quence : in the first place, because such a pigment as
ultramarine (with which I am chiefly now concerned)
can scarcely, except in minor details, be used with good
effect in a pure state ; and, secondly, because the quan-
tity of lime sufficient to insure the combination on which
the action of the vehicle depends, is so small as hardly
to affect the purity of the tint to any appreciable ex-
tent ; and, besides, the trifling loss of depth occasioned
by the admixture of white may be easily corrected by the
addition of black, which, though it imparts a certain grey-
ness to the tint when it is wet, does not affect its blue-
ness when the plaster is dry.
In preparing a tint of ultramarine in which the
pigment is to be used in as pure a state as may be,
I first make up the required tint with the least pos-
sible quantity of water; it is then diluted with the
sol ation of starch to the proper consistency, and a
s mall portion of lime added to it. The addition of the
lime has the immediate effect of curdling or imperfectly
solidifying the mixture. To remove this it must be
triturated in a mortar, worked with the palette-knife on
a slab, or, which generally is sufficient, stirred for some
time with a stiff brush until the consistency of cream is
attained. If the proper degree of fluidity should not be
restored, a little water may be added.
It is, of course, desirable that the adherence of pig-
ments with which starch has been mixed should in all
cases depend on the chemical combination of the starch
and lime ; but it is certain that to a limited extent the
glutinous quality of starch is sufficient of itself to secure
the adherence of the colour under circumstances in which
little or no chemical action can take place. As, for in-
stance, at the end of a day when the intonaco has be-
come quite hard on the surface, I have found small
touches and washes of pure colour (such as ultramarine
or the transparent oxide of chromium unmixed with
white) to adhere perfectly if applied with the solution of
starch, which, if applied with the water only, would
have dried on the surface of the intonaco in the form
of powder.
On the durability of the process it is premature to
express any opinion, as my experience only extends
over three or four years ; but as yet I am unable
to trace in those portions of the frescoes in the Queen's
robing-room painted by means of it the least symptom
of that whitened, bleached, and inharmonious look
which makes its appearance in blues, painted in the old
Way, almost
oaulirnsiqubcife.ufloLrs.:Ertvhaaesn,pi:iii:et hpas.
Rb.eAco.,me dry.—l remain,
Secretary to the Fine Ar'ts Commission. W.
DYCE.
f

STEREOCH ROME PAINTING. "ON SILICA
I AND SOME OP IT 8 APPLICATIONS TO THE
SuAbsßtarrnS.
ceof a lecture delivered at the Roval Institu-
tntion of Great Britain, April
Barlow, M.A., e7i,1854, by the Rev. J.
Vice-President and Secre-
• tary of the Royal Institution..ic
Silica is one of the most abundant substances known.
Quartz, common sand, &c., flint, chalcedony, opal,
variety of sand described by Mr. J. T.
(tWea.y, an
, da
may
respectively be taken as example& ofcrys.
talised and uncrystalised silica. Under all these forms
silica is capable of combining with bases as an acid.
Heat is, bosvever, essentially necessary to effect this
combination, a combination of which all the well.