Notes

The firings were time-consuming and complicated. To allow the tiles to cool down completely, the kiln was only opened 18 hours after being switched off completely. If four firings were done, as was normally the case, it could very well require a week or more to produce one tile as it took anything up to 24 hours of very gradual temperature increase to reach the 800°C or so required by the lustres.

The steps for each firing were basically as follows: first the glaze or glazes were applied and fired to about 1 090°C; then the lustres were applied and fired in turn, starting with the copper, which had the lowest melting point, followed by the gold which liquified at 825°C, i.e. 25°C degrees higher than the copper. At times a platinum lustre was also added if Bosch found the tile lacking in richness.

'There was definite method in the madness. One would expect to fire the higher temperature first and then the lower, but I found that the copper was reasonably stable and seemed to 'set' into the gold when both liquified, giving a beautifully integrated appearance to the final product.'

Previous experience was confirmed when he found that only certain combinations of colours were possible. 'The decoration did not work with a number of glazes I tried. I soon found that the lustre looked good only with darker colours such as black, dark blue, green and brown.'

The original intention had been to create a lustre surface that was very full and rich. 'The tiles demanded a great deal.'

Andree Bosch and Johann de Waal (1988) Esias Bosch, Cape Town: Struik Winchester, pages 46-47.