Monthly Tech-Tip | No tracking! No ads! |
The terra cotta casting body on the right, L4170B, normally casts really well (even better than the M370 on the left). Even though we have made this many times … today it is not working right. It took twice the amount of time in the mold to build up the needed thickness. It took three times the normal amount of time to release from the mold, when it finally did it wanted to turn inside out on pour (note the indent in the side). It also came out of the mold very soft and pliable. After drying, the surface, especially around the rim, has a hard film, it is difficult even to scratch. While the slurry itself is fluid and does not settle, it has the consistency of syrup. The problem is clearly over-deflocculation - this slurry is normally easy-to-deflocculate and performs very well. How did this happen? We are finding our new shipment of Darvan is more potent (therefore not as much is needed). Darvan has a shelf life, 2 years, the jar we were using was likely older than that thus more was needed.
Materials |
Darvan
A common deflocculant used to disperse ceramic suspensions to minimize their water content, a more modern material than sodium silicate. |
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Glossary |
Deflocculation
Deflocculation is the magic behind the ceramic casting process, it enables slurries having impossibly low water contents and ware having amazingly low drying shrinkage |
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