Items from John Black’s important collection of Dutch and English Delft were sold by auction today following his death. The details are here.
I visited Dr Black with the Oxford Ceramics Group (of which he was president) in 2013, when handling pieces from his collection gave insights into the workshop practice of the old tin-glaze potters.
For example, if you have seen a 17th century Delft dish in a museum you may have noticed three marks inside it, indicating that it was fired in a stack separated by three-pronged spurs. These dishes always have a narrow foot-ring, which gives an elegant finish to a fairly roughly made object; but seeing an old spur and having demonstrated to me how a dish fitted on top of it (above) made it clear that the reason for the small foot-ring was practical, not aesthetic. In the 17th century, as firing became more sophisticated, dishes were supported under their rims instead and the foot-ring could be made wider.
The plate above is unusual in having been decorated in all five of the pigments available to potters at the time: iron brown, copper green, antimony yellow, cobalt blue and manganese purple. Manganese mixed with cobalt produces a good black. Decoration in one, two or three colours is almost universal, the design easier to conceive and manage, with stronger identity and clearer differentiation, than decoration in four or five colours, which is rare.
The plate above (Netherlands, first quarter of the 17th century) caught my eye because the green in the balls is turquoise rather than the more yellowish green normally produced by copper in a lead tin glaze, which indicates that this plate was covered in an alkaline glaze. Alan Caiger-Smith, in Tin-Glaze Pottery in Europe and the Islamic World, reports the following Dutch glaze recipe from the mid-eighteenth century:
50 lb. dry sand
15 lb. potash
20 lb. soda
6 oz. manganese
Mixed, calcined, ground and sieved.
To this are added:
20 lb. lead
20 lb. tin
Calcined, and oxidized ground and sieved.
Such a glaze was 28 per cent alkaline (disregarding impurities), which would certainly have produced turquoise in the presence of copper oxide.
The trouble with copper oxide is that it blurs and it is difficult to make a sharp mark with it. Such a quality can be exploited by the designer, but from about 1700 it was replaced with a crisp green made by mixing antimony yellow with cobalt blue, which made an olive green as in the plate above (1720-40).
There were other insights, perhaps none so revealing as that offered by duplicated designs. In the example above, each plate is copied from the same pattern but they are different in treatment and interpretation. The painter on the left fills the space better and paints his motifs more decisively. In other examples the brushwork varies even more, between fluent and confident strokes and tight, awkward movements. It is clear that these Chinese-style decorations were often painted without understanding, almost as a set of meaningless abstract marks, and some of them look very odd indeed.
Dr Black had plates with bad faults in glaze or pigment and the fact that they had been sent to market at all tells you something about the economics of the potteries or the lack of supervision within them.
His little book British Tin Glazed Earthenware (2001) illustrates his collection.