ceraymics Posted April 1, 2014 Report Share Posted April 1, 2014 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 Link to comment Share on other sites More sharing options...
justanassembler Posted April 1, 2014 Report Share Posted April 1, 2014 start adding the darvan slowly, and check the specific gravity of the slip using a graduated cylinder and gram scale. Link to comment Share on other sites More sharing options...
ceraymics Posted April 2, 2014 Author Report Share Posted April 2, 2014 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? Link to comment Share on other sites More sharing options...
neilestrick Posted April 2, 2014 Report Share Posted April 2, 2014 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. Link to comment Share on other sites More sharing options...
ceraymics Posted April 8, 2014 Author Report Share Posted April 8, 2014 Thanks Neil, that's a good suggestion. Yes, the reaction with Darvan 7 is immediate, 811 is slower. Any thoughts on the quality of the slip when too much Darvan is added...would the cast pieces be weaker or stronger? Link to comment Share on other sites More sharing options...
Min Posted April 8, 2014 Report Share Posted April 8, 2014 From Alfred on dispersants for casting slips: http://claystore.alfred.edu/rawmats/resources/Dispersant%20Addition%20Procedures.pdf It's on how to test for the amount of Darvan to use. From the article it doesn't seem to make a difference between Darvan 7 or 811. Link to comment Share on other sites More sharing options...
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