hanor Posted September 20, 2022 Report Share Posted September 20, 2022 I made a white clay slip with specific gravity 180 yesterday for solid casting ! (idk how to say it in english , i mean slip weight waa 180g when water 100g) and I added about 1.5 times more of the the release agent(Sodium silicate )than usual.. But unexpectedly, the slip stuck to the mold. I thought this was a phenomenon when there was a lot of water in the slip. Or does this happen depending on the drying condition of the mold? plz help me... Quote Link to comment Share on other sites More sharing options...
Mark C. Posted September 20, 2022 Report Share Posted September 20, 2022 The mold needs to be very dry. The slip needs to be the right mosture content .Solid casting takes extra dry time as slip casting is usually hollow. The plaster mold can only absorb so much water for it to release the clay. Extra sodium silicate is not needed. PeterH and Hyn Patty 2 Quote Link to comment Share on other sites More sharing options...
PeterH Posted September 20, 2022 Report Share Posted September 20, 2022 9 hours ago, hanor said: and I added about 1.5 times more of the the release agent(Sodium silicate )than usual.. But unexpectedly, the slip stuck to the mold. I thought this was a phenomenon when there was a lot of water in the slip. Or does this happen depending on the drying condition of the mold? My guess at the physics of the process... Sodium Silicate is not a release agent, it's a deflocculant. It lets you make a workable slip with less water. But it's not the more the better, there is a sweet spot (which your usual casting slip will/should-be close to). Basically the mold sucks water out of the slip causing it to cast. The casting get slower as - - the cast walls get thicker (more resistance to water flow) - the mold gets saturated with water (and stops sucking) The first required patience (and perhaps optimization of slip properties). The second requires -- - either a thick mold which can comfortably absorb all the water that needs to come out of the slip to complete the casting. - or exceptional patience to wait while water evaporates out of the saturated mold, which then can start sucking again. - in either case starting with a really dry mold can only help. 10 hours ago, hanor said: I thought this was a phenomenon when there was a lot of water in the slip. That's because in that case the extra water may saturate the mold even when you are only casting thin walls. Quote Link to comment Share on other sites More sharing options...
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