Polish Archaeology in the Mediterranean (15.2003(2004))

OLD DONGOLA

SUDAN

APPENDIX 2
ANALYSES OF PIGMENTS
FROM THE CRUCIFORM BUILDING (B.III)
IN DONGOLA
Anna Nowicka
Academy of Fine Arts, Warsaw

The pigments were identified based on the
following:
— microscopic observation of samples in
reflected and transmitted light (water
smears);
— sensitivity to acids and alkalis;
— anion and cation determination in the
following microcrystaloscopic reactions:
P043‘ anion determination. Reaction with am-
monium molybdate, (NH4),Mo04, in 1INO.
medium (after dissolving sample in concenrated
HNO j and evaporation). Product of the reaction:
characteristic yellow deposit of ammonium
molybdate-phosphate, (NH4)3[P(Mo3O10)4].
Pb2+ cation determination. 1) Reaction with potas-
sium iodide, KJ (solution with concentration O,
1M) in diluted CHjCOOH medium (after
dissolving sample in concentrated HNOj and
evaporation). Product of the reaction: charac-
teristic yellow deposit of lead iodide, Pbl2; 2)
Reaction with four-ingredient mixture after first
dissolving the sample in HNOj and evaporation.
Mixture composition: saturated solutions of
CH3COONH4, KN02, Cu(CH3COO)2 and
30% CHjCOOH mixed in 1:1:1:1 proportions.
Product of the reaction: regular black crystals of
K2Pb[Cu(N02)6].
Fe3+ cation determination. Reaction with potassium
ferrocyanide, K4[Fe(CN)6], in HC1 medium
(after partial dissolution of sample in con-
centrated HC1 and evaporation). Product of the
reaction: blue fine-grained deposit of iron
ferrocyanide, Fe4[Fe(CN)6].
Fe31* cation determination. Reaction with potassium
thiocyanate, KSCN, in concentrated HC1
medium, after first dissolving sample in 4M
NaOH and evaporation. Product of the reaction:
red deposit of iron thiocyanate, Fe(SCN)j.

Fe2+ cation determination. Reaction with a,a'-
bipiridyl, after dissolving sample in HC1 and
evaporation.
Cu2+ cation determination. Reaction with potasium
ferrocyanide, K4[Fe(CN),d, in HC1 medium.
Product of the reaction: red-brown deposit of
copper ferrocyanide, Cu2[Fe(CN)6].
S2" anion determination: Reaction with azide
reagent. In the presence of sulfides, gas bubbles
are released and the reagent is discolored.
Sample no. 9: a) blue and b) red (interior
plastering, first layer)
a) Microscopic observation in reflected light (x 48):
Painted layer is light blue with apparent darker
crystals of turquoise shade.
Microscopic observation of water stnear in trans-
mitted light (x 640): Observed blue grains, color
intensity differing for various grain sizes (the bigger
the grain, the darker it is); pigment grains trans-
lucent, angular breaks; size reaches up to 0.07 mm;
Solubility in acids and alkalines: In 3M HC1,
cone. HNOj and 4M NaOH, the pigment does not
change either in cold acid or after heating.
Cu2+ cation determination: negative result.
Conclusion: The sample represents
Egyptian blue, CaCu{Si4O10}.
b) Microscopic observation in reflected light (x 48):
The surface of the painted layer observed in side
light looks like very fine, delicate brocade; it is not
mat. After the grayish-white film was removed from
the surface, the layer proved to be an intensive red,
dark with a brownish shade.
Microscopic observation of water smear in
transmitted light (x 640): Observed grains include
dark red, of bigger size, angular, semi-translucent,
some almost black; size — maximum 0.0045 mm.

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