Piedmont Pottery Posted March 20 Report Share Posted March 20 Some time ago I posted about challenges with wollastonite clumping. I have now found a process which is helping with this issue. I utilize one of these flour sifters when weighing out the wollastonite. I sift the material directly into a pan on the balance until I have the necessary amount. It's pretty low tech, but it works. Perhaps not feasible for large-scale batches, but I'm usually making 1-2kg batches of most of my glazes, and it works fine for that. Rae Reich, Magnolia Mud Research, Babs and 1 other 4 Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted March 21 Report Share Posted March 21 Do you have a particular reason for using wollastonite? I found swapping wollastonite for whiting and silica made no difference to glazes and whiting is much nicer to work with. Quote Link to comment Share on other sites More sharing options...
Piedmont Pottery Posted March 22 Author Report Share Posted March 22 22 hours ago, High Bridge Pottery said: Do you have a particular reason for using wollastonite? I found swapping wollastonite for whiting and silica made no difference to glazes and whiting is much nicer to work with. Wollastonite has a much lower LOI than whiting (1.6% vs 43.9%) and has a lower thermal expansion coefficient (9.0 vs 14.8) (data from DigitalFire). Wollastonite also provides silica in addition to calcium. My glazes are high silica/low expansion by design, and wollastonite gets me there. And finally, Wollastonite cost me $0.59/pound the last time I bought it, whereas whiting cost me $1.17/pound. I'm sure I could rework my recipes to substitute whiting, but there is a certain amount of inertia involved in doing that, as I'm generally happy with the way my glazes are behaving on my clay. Hulk and High Bridge Pottery 2 Quote Link to comment Share on other sites More sharing options...
Min Posted March 22 Report Share Posted March 22 For sure you can get the chem to match using silica + calcium carb for wollastonite. I've done the reverse with recipes calling for calcium carb and subbed in wollastonite and reducing the silica in the recipe so the formulas match. What I found was the wollastonite versions melted noticeably more. Some recipes won't show a difference, depends on glaze mobility and how much CaO is involved. I think another factor is the mesh size of the silica being used in the recipes. Perhaps very fine silica, ie 90 micron compared to 45 micron would show a difference in the melt if used with calcium carb? I've always thought of wollastonite as being like a frit, albeit a lumpy one, it melts really well and with minimal LOI. Hulk and Piedmont Pottery 2 Quote Link to comment Share on other sites More sharing options...
Mark C. Posted March 23 Report Share Posted March 23 When I have lumpy materials I just weigh them dry and put them in my shop blender with a bit of water and dump into the wet glaze batch -just put it on magarita mix for a few minutes . Makes anything smoth in minutes but wait theres more- it liquifies and is as smooth as silk in mere minutes and you to can pick one up for just one low payment at any thrift store Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted March 23 Report Share Posted March 23 Interesting that pricing is the opposite in the UK, whiting £1 a kg and wollastonite is £2.46 a kg. Probably based of what's in the ground locally. Melting better is a good reason to use it. I am yet to find any proof that whitings LOI causes issues with glazes, it starts at 700c (1300f) and over by 900c (1650f) Quote Link to comment Share on other sites More sharing options...
PeterH Posted March 23 Report Share Posted March 23 5 hours ago, High Bridge Pottery said: I am yet to find any proof that whitings LOI causes issues with glazes, it starts at 700c (1300f) and over by 900c (1650f) A slight quibble ... Digtalfire seems to think there can be issues when "late gassers overlap early melters". https://digitalfire.com/picture/huctibegac ... 1400F=760C So perhaps whiting can/does cause issues when used in combination with some early-melting ingredients, such as frit 3124. Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted March 23 Report Share Posted March 23 I agree if you were only using frits then maybe it could be an issue to add whiting but at cone6 - cone10 I just don't see it. Even in the only related post underneath he is swapping talc for dolomite "While dolomite has a far higher LOI than talc it starts releasing the gasses of its decomposition much earlier and finishes well before talc." That's a cone6 recipe with 17% frit. Even looking at his melt tests with frits at 1650 I can see 5 that are not exactly melted. https://digitalfire.com/project/comparing+the+melt+fluidity+of+16+frits Quote Link to comment Share on other sites More sharing options...
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