EXAMINATION OF CERTAIN SPECIMENS OF
MURAL PAINTING AND PLASTER
FROM AK-TEREK, KARA-SAI, KHADALIK, MÎRAN, ' MING-OI',
SIR ARTHUR CHURCH
Two specimens from M ran, now numbered i and ii.
On a backing of loess strengthened by means of the leaves and stems of the common reed (Plaragmitcs communis), there was spread, and that very skilfully, a thin flat coating of impure burnt gypsum which had been made into a cream with water. Over the whole of this nearly white ground a layer of a pale pinkish pigment had been distributed. The pink colour is due, not to any organic substance, but to ferric oxide (Fe20.3). 'There is a little calcium sulphate in this pink layer, but this has been derived from the wet plaster on which the pigment had been spread, and not, as I imagined at first, from an admixture of plaster of Paris with the pigment. Nor can I find definite evidence of the use of any organic binding material, such as gum or size, in the coloured layer. What organic matter is present in the painted plaster is probably derived from the reeds used in the backing, and is accidental.
Upon the uniform pink layer just described, designs were painted in these three colours—pale green, pale yellowish brown, and grey. The green colour is derived from malachite, a basic copper carbonate ; the yellowish brown is due to an impure ochreous earth ; the grey to carbon in the form of what may be called Chinese ink. As Chinese ink is composed of soot and size, it is quite possible that the other pigments may have once contained some size, so that the method of painting used at Mirân would have resembled ordinary tempera, but the chemical evidence on this point is far from decisive. In any case this painted fragment differs from all European frescoes in that its ground was plaster of Paris, and the attachment of the pigments to the surface was not dué to the production of a binding film of calcium carbonate.
One specimen from Kluidalik, now numbered iii.
Upon a backing of a rather clayey loess admixed with fibre is a thin smooth layer of plaster of Paris, superficially tinted with a pinkish ferruginous pigment. The white layer dissolves in acids without effervescence, also in pure water : the solution is one of calcium sulphate. The painting has not been executed upon a ground of slaked lime and sand as in true fresco. The vegetable fibrous material here consists of the leaves and stems of the common reed. There is no distinct evidence of the use, as a binding material, of any gum or size. The backing contains a little sulphate of lime, but not enough to indicate an intentional addition of plaster—in fact, not more than would have penetrated the backing from the wet plaster laid thereon.
One specimen from Kheidalik, now numbered iv (labelled ` found with Kha. i. frescoes, case 3 ' ). This is modelled in loess with fibre, but has originally been coated with plaster of Paris.