Quote:
Originally Posted by Aktungbby
sanding or scraping excess clay to create a smooth clay mold?
|
That would be done after this ..
Quote:
Originally Posted by Eichhörnchen
Searching out the imperfections?
|
Yep, you got it, it is about quality control of the outer clay form!
Both men had mirrors and looked up and down the barrel to spot excess clay, using candles for illumination.
A hole in the outer mantle of the cannon's form would be ugly later, but could be easily removed with a rasp/file.
But any protrusion of clay
towards the inner form would cause cavities and weaken the mantle, maybe exploding the cannon in the operator's face later. Because of using bad clay and a lack of control a lot of cannons had to be scrapped after casting, or the cavities were not found in the cast, leading to disastrous accidents.
Clay of various compositins (fractions) has to be used, mixed with stabilizers and (indeed) horse pee..
The later inner clay core for the bore could be examined easily outside, smoothed, and only then lowered into the outer form, later.
But controlling the outer form had been a problem.
First the outer part of the cannon was formed in clay, with all decorations etc., the thing looked like the later cannon cast would.
Then charcoal was applied on the wet surface.
Then the outer form was created, appying thin, fluid clay in thin layers around the cannon form, adding more material and less fluid with every layer.
Then the whole package was stabilized with wood and rope, as seen in the picture, and vertically lowered in the pit.
One of the masters would then carefully scrape away the inner form of the cannon from the outer form, until he reached the dark charcoal layer.
When this was done, the later outer form of the cannon, imprinted in the outer form, was controlled with candles and mirrors, to rule out shrinkage cavities and so on – which can be seen here.
Later the bottom end form would be mounted on the lower end, then the clay core for the bore would be inserted from above.
Then the whole pit would be filled with sand, to stabilize the form and keep it from breaking during the later cast.
Usually several forms (up to four) were placed, and cast together in one pit.
The composition of the molten bronze and how it was prevented from separating in the melt was another problem..
And so on ...
Aktung was so close, but i'd say it is
over to Eichhörnchen 
P.S: thinking about how complicated, time and material-consuming this was just to produce ONE cannon ... we are currently trying to create one for a museum. You won't believe which problems you can encounter
