Gilding 19th century in PortugalApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2018-10-29 10:05:58 ...
Most recent comment 2018-10-29 09:38:00
Gilding
I'm reading a 19th century Portuguese treatise on gilding. The master gilder that wrote it was called Francisco Liberato Telles de Castro da Silva. He was in charge of the restoration of the gilded woodcarvings of the church of Madredeus, in Lisbon.
He advocates a recipe for the red bole that puzzles me:
1kg Armenian red bole + between 120-150g of graphite powder + between 120-130g of sanguine hematite. This mix should be ground in pure water (and allowed to dry afterwards? The original text isn't clear on this), then mixed with a spoonful of olive oil and ground again. Just before use, this mix should be ground with a weak solution of rabbit skin glue and another spoonful of olive oil.
I have two questions:
If the original mix is allowed to dry before adding the olive oil (as the text strongly suggests) then a spoonful wouldn't be enough to wet the bole - so perhaps he didn't mean to fully dry but just to allow some of the water to evaporate, so the oil could be added to the thickened paste.
Could this very small amount of olive oil be there just as a plasticizer? Wouldn't the fact that olive oil is non-siccative create problems with the drying of the mordant and also with the burnishing? On the other hand, I know that the most beautiful burnishing is achieved when the bole is just before fully dry (a few hours after, not a few weeks after)... maybe the small amount of olive oil replaces that necessary small amount of humidity, allowing top level burnishing to be done after all the water in the bole evaporated?
Many thanks!
Nelson
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Moderator Answer
(brian baade)
This indeed an interesting recipe. Generally, graphite was
added to facilitate burnishing when the iron oxide does not have a clay
component (like the hematite here). However, the Armenian bole would contain
clay. I do remember reading that some bole recipes contained tallow and other
greasy components so perhaps the olive oil is not as peculiar as first seems.
This question exceeds my knowledge and I will forward it to
someone with more experience in this area.
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Moderator Answer
(brian baade)
I have spoken with an expert gilder who is also a
conservator of frames and we both think that there is something missing from
this recipe. It is certainly possible
that they included some fatty material (olive oil in this case) to facilitate
burnishing, etc, but there needs to be a preponderance of an aqueous component
for this to be used for water gilding. The recipe would not even work for mordant
gilding given the “non-drying” nature of the olive oil. We will get back to you if we discover anything additional.
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