Historical Painting Techniques, Materials, and Studio Practice

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plaster consists of lime combined with an aggregate of subangular quartz in

a ratio of 1:3. It is generally more yellow and less well prepared than the

plaster fo r the earlier decoration, with large lumps of unmixed calcium car­

bonate clearly visible.

It is now difficult to establish the sequence of application of the plaster, since

surface fe atures have been completely flattened by the detachment process

(Figs. 3, 4). Examination under raking light of the surface of the east wall

paintings (now transferred to the west end) does, however, indicate that plaster

joins may originally have run along the upper edge of the central border and

the lower horizontal of the cross in the upper register. This indicates that

generally the plaster may have been applied in broad horizontal bands, rough­

ly corresponding to scaffo ld lifts. However in the east recess of the south wall

there appears to be a vertical join between the Harrowing of Hell and Noli me

Tangere, suggesting that in this area at least a fu rther division was considered

necessary.

Preparatory techniques. A preparatory sketch in red iron earth was used to set

out the main fe atures of the composition. Unlike the twelfth-century painting

wherein both a sinopia and then fu rther preparatory drawing on the final

plaster layer exist, in the thirteenth-century scheme the preparatory drawing

is confined to the final plaster layer.

Direct incisions into the plaster are also clearly visible, such as the fine, sharp

incisions that outline the curls in the hair of the figure at fa r right in the

Entombment and the hair of St. John in the Deposition.

Pentimenti. An interesting alteration discovered during the detachment pro­

cess-and presumably visible on the reverse of the thinned plaster layer-was

that above the horizontal arm of the cross in the Deposition was a sketch fo r

the sun and moon, which are symbols more usually associated with the Cru­

cifixion (27).

Pigments. The present research has established that the original palette in­

cluded: natural ultramarine (3Na20·3Al203·6Si02·2Na2S); vivianite (Fe3 +

2[P04L'8H20); copper chloride green; cinnabar (HgS); hematite (Fe203); yel­

low iron oxide (Fe203'H20); lead white (2PbC03·Pb[OHl2); lime white

(CaC03); charcoal black (C).

Binding media. The inclusion of lead pigments in the palette makes highly

likely the incorporation of organic binding media as part of the original

technique but, owing to the previous conservation interventions, it was not

possible to confirm their presence.

Application. Preliminary drawing in red ochre was fo llowed by blocking in of

the basic background colors. Oakeshott considered that the powerful black

outlines, which are such a ma jor feature of the scheme, were also painted at

this stage and were thus more firmly bound by the carbonation of the plaster

(28). The stratigraphy is remarkably simple, with one or at most two paint

layers applied directly to the plaster (Tables 2, 3, 4, 5). In some cases the final

paint layer was applied in thick impasto, and it seems likely that here an

additional binding medium was used.

Pigment alteration. Although the background colors of the scheme are now

red and green, it seemed much more likely on the basis of comparisons with

other paintings of the period that red and blue would originally have been

used. Analysis indicated that this was indeed the case: the present green color

is due to the alteration of some of the original blue pigment (vivianite) to

fo rm a yellow alteration product.

The alteration of a lead pigment is evident in the fo rm of black spots on the

paint surface throughout the scheme, and analysis confirmed the presence of

a dark red/brown lead-based material. In wall paintings elsewhere where this

type of alteration occurs, the alteration product has been fo und to be platt­

nerite (lead dioxide) (29). In the Holy Sepulchre Chapel however, analysis by

Historical Painting Techniques, Materials, and Studio Practice