Mike.Kelly Posted October 24, 2018 Report Share Posted October 24, 2018 OK So I have not been able to narrow down what causes the different results. I have tried thin coats, thick coats, heat drying, drying naturally, opening slowly, opening fast, and combinations of all the above. I also wondered if it might be due to the dry/wetness of the clay, but both of these pieces came from the same bag. What I am after is the little cracks not the big cracks. Any ideas why I am getting different results? Link to comment Share on other sites More sharing options...
liambesaw Posted October 24, 2018 Report Share Posted October 24, 2018 It's all about how dry it is. You can encourage cracks by scratching the surface before applying sodium silicate too. More time under the torch are deeper cracks Link to comment Share on other sites More sharing options...
glazenerd Posted October 24, 2018 Report Share Posted October 24, 2018 The chemistry behind sodium silicate has been somewhat lost in modern pottery. The reaction of sodium silicate at one time was measured in " degrees twaddle." I think some places in the UK still use this measurement of potency. Once upon time, sodium silicate was sold in 75 or 150 degrees twaddle. The lower degree being used for minimum thinning of slip, or often used in colloidal chemistry. 150 degree twaddle was obviously twice the potency as 75 degree twaddle. So it was used to thin heavy slips, or in half proportions. Sodium silicate has a more important role in slip besides "thinning." ..more chemistry for another day. that said: I have tried for several years to pin down the potency of sodium silicate sold in the USA- with zero result. However, from testing and results: most likely 150 degree twaddle. So experiment: dilute it by 1/3, 1/2, and 2/3rds with water and see which result you like. You can also use aloe (sold by the gallon for $15) organic, burns off. T Link to comment Share on other sites More sharing options...
liambesaw Posted October 24, 2018 Report Share Posted October 24, 2018 5 minutes ago, glazenerd said: The chemistry behind sodium silicate has been somewhat lost in modern pottery. The reaction of sodium silicate at one time was measured in " degrees twaddle." I think some places in the UK still use this measurement of potency. Once upon time, sodium silicate was sold in 75 or 150 degrees twaddle. The lower degree being used for minimum thinning of slip, or often used in colloidal chemistry. 150 degree twaddle was obviously twice the potency as 75 degree twaddle. So it was used to thin heavy slips, or in half proportions. Sodium silicate has a more important role in slip besides "thinning." ..more chemistry for another day. that said: I have tried for several years to pin down the potency of sodium silicate sold in the USA- with zero result. However, from testing and results: most likely 150 degree twaddle. So experiment: dilute it by 1/3, 1/2, and 2/3rds with water and see which result you like. You can also use aloe (sold by the gallon for $15) organic, burns off. T This one on Amazon shows: Concentration: Sodium silicate: 37% Wt.% (28% silica + 9% sodium oxide) Water: 63% Wt% Appearance: Thick clear to hazy white liquid. pH: Approximately 11.3 Specific gravity: 1.39 g/cm3 (20°C), 41° Be, 11.62 lbs/gal Dont know how that converts to twaddle though. I've found the science supply and concrete flavored brands are the most forthcoming with their formulas Link to comment Share on other sites More sharing options...
glazenerd Posted October 24, 2018 Report Share Posted October 24, 2018 SPG 1.39 x 1000= 1390 - 1000 = 390 divided by 5 = 78 degrees twaddle. Surprised actually. PH 11.3 anything over 11 PH is classified as caustic: in this case caustic soda (sodium) using a torch to accelerate drying is not really a good idea. Like any good acid or caustic alkali: the length of time for reactions to occur will have more effect on outcome. Diluting with 1/4 to 1/3 water to lower the PH to around 10 pr so would minimize the reaction as well. The length of time before stretching the form would also be a factor. sodium is a drying agent: used for centuries to cure pelts, dry meats, etc. In part some of the chemistry going on here. Link to comment Share on other sites More sharing options...
Mike.Kelly Posted October 24, 2018 Author Report Share Posted October 24, 2018 Thanks for all the responses. I haven't tried diluting yet so will give that a go in the next couple of days. Link to comment Share on other sites More sharing options...
Min Posted October 24, 2018 Report Share Posted October 24, 2018 @Mike.Kelly, for smaller cracks try mixing a little sodium silicate into some slip. I've done this with both a porcelain slip over a red clay plus a slip made from the claybody. The more sodium silicate in the slip the larger the cracks, try about 2 TBS sodium silicate in a cup of slip, if the cracks are too small add more. Link to comment Share on other sites More sharing options...
glazenerd Posted October 24, 2018 Report Share Posted October 24, 2018 Insight references sodium silicate as 50.78% sodium and 49.22% silica. SG 2.40. Or 280 degrees twaddle. Given all the sources on the web, the potency of sodium silicate is going to vary from region to region. Which in part might explain different results from potter to potter. Link to comment Share on other sites More sharing options...
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