After a long break, mostly due to guilt at not finishing the two plates that languish in my kitchen cupboard, I have started decorating plates again. This resurgence of interested was prompted by a post by Aliette of Stormhold quite a few months ago. She posted a rather nice plate (13th Century I think) that sported a simple cat motif. While looking for the details of the original I stumbled upon something much more interesting, a 12th century peacock dish from Syria (Figure 1).
Fig 1: Peacock plate from Syria. 12th Century. Accession number: 29.160.17. Metropolitan Museum of Art
The back of the dish is plain and shows minor green staining. Interestingly, when stood 'flat', the plate appears to slant towards the left of the peacock. The rainbow luster around the edge of the plate and around the breast of the peacock bothered me initially. In my limited knowledge of ceramics, I associate that effect with modern day fairies or ballerina ceramics, not 12th century dishes. Looking at the unstained head of the peacock where the plate is the whitest there is no iridescent coloration. So, the two most likely causes are 1. a pigment used to outline the peacock and add decoration to the edge of the dish as been changed to create the irridescence, 2. groundwater or whatever stained the dish orange transported chemicals onto the plate to create the irridescence.
Cause 1 - pigment conversion
I have sifted through the Met's Syrian 12th century ceramic collection and found a fragment of a bowl (Figure 2) featuring a bird which has a similar white outline of the wings and features to the peacock. Given there is no trace of a decorative motif on the rim of the peacock plate this suggests that the void around the wing was intentional not the result of alteration of pigment causing the iridescence.
Fig 2: Fragment of a bowl. late 12th - first half 13th century. Composite body, underglaze painted. Syria. Accession number: 1978.546.9 The swan (?) depicted has voids outlining it's primary leg and wing.
Cause 2 - pigment discoloration
I have examined the images of most of the Met's Syrian ceramic collection and have found others with the iridescent staining (Figure 3 and 4). Both plates feature blue and green images similar to the peacock in colour. The Faun? (Figure 4) has the best example of irridescence as it only appears on areas that also exhibit orange staining. The likely cause of the iridescence is groundwater interacting with the underglaze chemicals (copper?) and causing the staining.
Fig 3: Syrian (Raqqa) plate featuring a Sphinx. late 12th- first half 13th century. Made out of stonepaste, under-glaze painted under a transparent, greenish colorless glaze. Accession number: 13.219.1. Metropolitan Museum of Art.
Fig 4: Syrian (Raqqa) plate featuring a faun? Stonepaste, under-glaze painted. Accession number: 56.185.5. Metropolitan Museum of Art.
So. Having made the conclusion I can ignore the iridescence, I can now happily paint a white plate with a beautiful blue and green peacock.