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Epsom Salts question


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Hello everyone - epsom salts seems to me to work like magic to me.  Got some slip or glaze that's too runny, add some epsom salts and voila it's fixed!  

Stupid question  time - does it affect the final effect of a glaze / slip etc?  ie: is it possible that too much epsom salts can effect the final outcome of a glaze?

I've not really experimented much with this magical stuff - can it help glazes in other ways?

Any help/advice much appreciated

thanks!

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The amount you add to a glaze in order to flocculate it properly isn’t significant enough to affect the chemistry, no. If you add too much to a glaze batch, it’ll clump up to the consistency of your reclaim, and at that point you can’t apply it to a pot. 
Sue Macleod is the queen of teaching about glaze flocculation. Her blog here is an excellent one. 
https://suemcleodceramics.com/how-to-make-a-saturated-epsom-salt-solution-to-flocculate-your-glazes/

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Hi E!

Good question, hadn't thought about any influence magnesium sulfate might have on my glazes...

My guess is the sulfate part burns away in firing; from there, MgO is tracked in the glaze software I'm using - it's a low expansion oxide, yes? The amount I'm using to gel glazes is very small, my second guess is the magnesium part is not significant.

It is magic! ...fwiw, I set my specific gravity before adjusting thixotropy (usually with Epsom salt, was using vinegar as well...).

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57 minutes ago, RICHARD SE said:

Hi all. Another question about Epson salts is what sought of amount would you start adding to Porcelain casting slips which is to thin for pouring. Thanks 

Others with more experience will chime in, but I'm not sure I would add it to a casting slip, which I assume has already been deflocculated? If that's the case, I would either let the slip dry out or add more dry material to the slip to correct the problem.

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What is the specific gravity of the slip? Any chance you have just over deflocculated it? I agree with Neil about correcting why it is thin rather than trying to fix it with epsom salts. Something is off, either SG or over deflocculated. Post the recipe, including how much water you added.

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Hi min.  I was just wondering if I made the slip too thin ,can I use Epsom salts to thicken it up. I am new to learning slip casting

I started with A 10 kg block of porcelain then add small cubes to 1.8 litres of water mixed thoroughly  p.g was 175 

I added 10 ml sodium silicate and a few drops of dispex 

I am doing viscosity test now 

when I bought pre made casting slip the p.g I checked was around 175 

also I done test on viscosity by draining 200 ml through syringe with a 3 mm hole and took 70 seconds to empty 

so I am aiming for a similar result with my home made slip

am I on the right track

regards Richard 

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Hi Richard,

A few thoughts, first off not all throwing bodies make good casting slips, amounts of plasticizers in porcelain throwing bodies can be too high for the same body to cast well.  Casting bodies need just enough plasticity for the slip to pull away from the plaster walls. Re sodium silicate, for simplicities sake let's say your 10 kg block of porcelain contains 20% water therefore that leaves you with 8kg of clay material. Really rough ballpark amount of sodium silicate would be 0.2% of dry material weight so that puts it at 16 grams. I don't know how much your 10 ml of sodium silicate weighs but I'm guessing it's going to be more than that. Other variable is sodium silicate comes in different strengths so that can mess calculations up also. Your specific gravity might be okay where it is but might need to go higher, try leaving the lid off the slip and let some of the water evaporate out. There isn't one magic number for what the specific gravity should be, your mix could very well need a different one than the commercial slip you used. What does it cast like, slow to release? Does the slip in the bucket form a skin fairly quickly when you stop mixing? If you stick your hand in the slip with your fingers spread open does the slip form webs between your fingers?

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hi min thanks very much for your time and effort 
10 ml sodium  = 14 grams in weight.  According to the bottle label  of sodium I have ,10 kg
 block of porcelain contains 20% water therefore that leavesyou with 8kg of clay material. Really rough ballpark amount of sodium silicate would be 0.2do you mean 2.0 grams per kilo

it doesn’t seem to form a skin when I stop mixing at all, Actually it doesn’t form a skin at all after whatever time I leave it And it doesn’t seem to form water on the surface after a day or so either 

i have poured  a cast this afternoon and the only thing is that I let the slip set for 7 minutes and it formed quite thick as in 4 mm ,I am after 2 mm thick for the transparency for the light shade ,it poured quite well and didn’t leave any ripple effects at all (the porcelain clay I am using is a translucent called COOL ICE  from a manufacturer here called CLAYWORKS )which I have got with the factory made slip previously with 7 minutes of time   I will try another pour tomorrow and set for maybe 4 minutes and see if I get the 2 mm I am after

Thanks very much again min

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22 hours ago, Callie Beller Diesel said:

The amount you add to a glaze in order to flocculate it properly isn’t significant enough to affect the chemistry, no. If you add too much to a glaze batch, it’ll clump up to the consistency of your reclaim, and at that point you can’t apply it to a pot. 
Sue Macleod is the queen of teaching about glaze flocculation. Her blog here is an excellent one. 
https://suemcleodceramics.com/how-to-make-a-saturated-epsom-salt-solution-to-flocculate-your-glazes/

Thanks Callie - I had watched that video yesterday, hence my question about whether it affects the final outcome of a glaze.  Her videos are brilliant.  So simple and well explained.  A fantastic resources

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