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Hi,

 

I'm mixing  VC vitreous white /\6 casting slip, which calls for 3.5% Darvan 7. Unfortunately I cannot get Darvan 7 any longer and was sold Darvan 811.

I'm trying to find out how much DArvan 811 to use as it is "much stronger"....very vague. Research on the internet, and phone conversations with reps from the manufacturer (Vanderbilt) and Laguna haven't helped much as they say "to add little by little", "don't use too much", "wait at least 24 hours after adding Darvan 811, as it works much slower than Darvan 7". I have done all that but the slip still feels thick and almost gooey. I don't know how much Darvan is too much.

Does anybody have had this experience, and found a solution?

 

Vitreous white /\6

grolleg          25

EPK              25

Kona F-4      30

frit 3124         4

flint               16

bentonite       2

H2O           40-50%

darvan 7      3.5 grs      darvan 811 ?????

 

Thanks,

raymonde

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justanassembler, thank you for your response. How slowly is "slowly"...by the drop, 5 drops at a time, how many do I start with...? Since I was told by the manufacturer to wait at least 24 hours, if not longer, between additions, it'll be a lengthy process.

A specific gravity of 1.75-1.85 is what I should aim for?

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Whether it's drops or teaspoons will depend on how much slip you're making.

 

I've never heard of a deflocculant taking 24 hours to react. I've used Darvan 7 and Sodium Silicate over the years and it's always been an instantaneous reaction. Do a small test batch, like a quart, and add the Darvan a drop at a time and see how quickly it reacts. It may be that you can get it darn close right away, with just minor tweaking after 24 hours.

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