Date and Time: February 23rd, 2015 at 10:00 am
Location: Chandler room 260, Columbia University
Subject: Sand Casting
Recipe from Folio 80V
<title id="p080v_a1">Casters of small tin work</title><ab id="p080v_b1">They usually cast from solder the things that should not become hollow, because these require fine and soft tin. However, these things would not otherwise lose their coat or become hollow if they are mixed or include glass tin in them, just like they mix a little [glass tin] in the soft tin. They engrave their work on stones of which the sharpening stones[431] or barber's files are made. These are found in great flakes near the mountains, and resemble slate. You can find these [rocks] in three colors: one reddish, that is not as perfect as the others because it does not sustain heat; [another] one is the color of dark slate, and the other is whitish. When they work a relief, first they print it on paper maché[432][433], which is one finger thick, to serve as a pattern. After planing the stones and rubbing them together, they use a compass or little iron [434][435]tools to engrave their figures. They make their moulds with three or four stones, to make a circle or a square with the stones which join perfectly because the stones are of equal size. Before casting, they rub the mould over with tallow, and it [the mould] absorbs it quickly because it is hot. [Then, having [put] fine powder of quicklime into a cloth, they rub the mould using pounce[436][437][438][439] in beating the linen on top, then blow it a little on top; this prevents bubbles [from forming].?] The main thing is that you make some vents. If the work is big, they do as it is shown [on the picture]. They make a hole in the medal, somewhere where it is least visible, and with a bit[440] they pierce the mould on the side of the medal. And if they want their work to last, they pierce [it] somewhere and fit in a piece of cork. Lead or tin will not damage it. </ab>
<note id="p080v_c1a">Make sure the pegs of your frame fit in easily so it will open with ease without moving anything else. Your tin box moulds should fit well, and the table should be very flat. </note>
<note id="p080v_c1b">Try to engrave with distilled vinegar.</note>
<note id="p080v_c1c">Try calcinated oyster shells; they are said to be excellent for moulding.</note> [image]
Discussion and first approach to the recipe
We discussed the recipe for a long time, trying to identify the function of the calcinated oyster shell.We explored two possibilities:
- Oyster shell could have been used as sand
- Oyster shell work as a separator agent in this recipe.
In both cases, we believe that the author never experimented himself the use of oyster shell, but he encourages the reader to try them.
We examined the location of the note about oyster shell in the marginalia of the folio finding a possible correspondence with the text passage about the sand casting process. However, the author mentions ‘quicklime’ in the text recipe as a separator agent. We immediately connected the oyster shell note with the term ‘quicklime’ considering that the note could be a suggestion of an alternative separator agent.
We proceeded using the oyster shell in the form of a slaked quicklime (available in the lab.) as a separator agent during the sand casting.
Procedure
Before starting the procedure with Joel’s assistance, we worked with a chisel to smooth the edge of our plaster molds. We ended using one of our mold and Joel’s medal for our experiment.We decided to use brick dust as a sand, while Sal ammoniac water was used as a binder. Composition of Sal ammoniac:
- 30 grams ammonium chloride
- 900 ml water
- 0.8 grams of brandy
Meanwhile we began to grind the oyster shell powder as fine as possible. We positioned our plaster mold and the medal on a silver plate. Then we framed both objects with the smallest wooden box available in the lab. After that, we began pouncing the ground oyster shell on the top of the objects.
Once the brick dust was ground enough, we added a few teaspoons of binder until the sand was staying clumped together after holding it in our hands.
We covered the objects of the sand mixed with the binder until the edges of the box. Then, we applied pressure with the body weight in order to pack tightly the sand. After that, we flipped the box with the use of another silver plate. We put some pressure on the reverse of the object too with the use of a hammer handle. We finally removed the object from the sand. As a result, the separator worked well for the details of both objects, but it didn’t help with the edges of the two medals. In both cases, the edges came out uneven, and the sand flaked. A layer of white oyster shell powder was still present on the mold.
We proceeded pouring the tin that Jef cut and then melted in the fume hood. We poured the melted tin in one of the mold, but we didn’t have enough to cover completely the second mold.
After 20 minutes we removed the tin from the mold. The result was not good. The tin didn’t catch all the details of the two objects, and its shape was uneven. We believe that the oyster shell as a separator agent didn’t work as expected. For the next experiment we are planning to use oyster shell slaked quicklime as sand.
After completing the procedure, we realized that we forgot to rub the two molds over with tallow. So we started a second experiment rubbing one of the mold with tallow heated by a candle. The experiment will be completed during the next class….
