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An early polychrome Delft bowl

5
Voorwerp

An early polychrome Delft bowl

Afmetingen
140mm diameter 90 mm high
Collectie
publiekscollectie
Unieke code

Reacties 5

Dear Jan van Zijl, This is an early, before 1640, tin glazed bowl. It is posible Delft but not certain. Unfortunately very fragmentary and obvious an excavated piece. This is just a blue and white bowl with ' paarse trek ' and certainly not an early polychrome bowl with red. As it was in the ground for a long time the darker blue painted sections were stained and changed in this red looking colour.

Dear Edwin

Thank you for your reaction

To my knowledge 'Paarse trek' was achieved by mixing Cobalt with Iron Oxide OR it was achieved by painting in Manganese Oxide. Usually the blue cobalt decorative pattern was merely outlined. Painting in blocks of Manganese purple was not really common until 1680.

The interesting thing about this bowl is that the red/brown decoration is not just used to outline a cobalt blue design but is used to paint in whole blocks of colour. The red area when analysed by X-ray spectography shows the existence of iron haematite mineral ONLY. There is no cobalt present in these red areas.

It would suggest that a red clay was used to paint in the red/brown design elements

Dear Jan van Zijl, Thank you. I am not a chemist but I only have some knowledge about excavated early Delft. I have seen this discoulorasation many times. Many Delft fragments are found in old privy's. The enviroment / contents of a privy is very aggressive. These chemicals / acids oxidize the top layer of of Dutch tin glazed ceramics after 200 or 300 years. Therefore the more thickly painted blue sections will discolur and can turn into a red / brownish colour. It is only the top layer, when scrubbed with ktichen soap ( vim ) or a light sandpaper the red colour will disappear immediately and the blue, original, colour will appear again. With kind regards, Edwin van Drecht. ps. You can also contact Prof. Norman Tennant.

Dear Jan and Edwin,
I think this is a very interesting object and conversation and I will discus this with my collegues of the archaeology-department in Delft. Up until now I don't know if a piece like this is in the archaeological collection of Delft. If I find something I will let you know by e-mail.

I agree with Edwin, this is a very common discoloration due to the very acid environment in a cesspit. I've seen it often on finds in Antwerp.

Regards,