Natania Posted July 12, 2011 Report Share Posted July 12, 2011 Someone recently recommended that I add a frit (3134 was suggested) to my slips to aid in adhesion/ melting when I paint them on bone-dry ware. Does anyone have an idea about what percentage would be good to start with? To complicate things I usually buy my slip wet by the gallon....? So I'm not sure how to calculate percentages this way... Thanks! Link to comment Share on other sites More sharing options...
Guest HerbNorris Posted July 13, 2011 Report Share Posted July 13, 2011 Since you want to add frit as a percentage of the dry materials in the slip, you have a little problem, as the slip comes mixed. How to know (to a usable accuracy) how much clay has been suspended in the water to make the slip, so that you can add frit as a percentage of this dry clay? There are three ways you could do it, two of which are pretty accurate, one of which is trial and error. Accurate (but slow): 1. Weigh a measuring container in which you can accurately measure one cup of slip. (I have suggested one cup, as you say you get your slip in gallons, so I am assuming a cup measure would be most handy, rather than a metric graduated cylinder, etc.) Write this weight down, and don’t lose it!! 2. Mix your gallon of slip quite thouroughly, using the best mixing equipment you have, a drill/squirrel cage, impeller, etc. Whatever you have, use it to mix the slip very well. 3. Immediatley pour, as accurately as you can, one cup into the measuring cup. 4. Now either let the slip dry completely, either on it’s own, or accelerate the process with a hot plate, drying cabinet, warm oven, etc. You need all the water out of the sample. 5. Once the sample is completely dry, weigh the cup with the dry clay in it. Write this number down! 6. Subtract the weight of the cup alone (you wrote that down, didn’t you?) from the weight of the cup/dry clay weight. 7. The result of this procedure gives you the weight of solid material (clay plus any colorants) that is dissolved in one cup of slip. 8. Now that you know the amount of material in one cup, you can determine the total amount of dry material in the gallon of slip (or any amount of this slip, for that matter), Since there are sixteen cups in one gallon, just multiply the amount of dry material in the one cup sample you dried, and multiply by sixteen. Let’s say there is 4.3 ounces of dry material in your dried cup. (just a guess, I have no idea). 9. Multiplying 4.3 ounce by sixteen (4.3 X 16 ) gives you 68.8 ounces of clay suspended in the gallon of slip. 10. Now you can figure your percentage(s) for testing. To add one percent of frit, just multiply 68.8 by .01, giving you 0.688 ounces of frit to add to the gallon. (0.7 is close enough). To add more in percentages, just multiply 0.688 by the percentage you want. If you want five percent, you would add 0.688 X 5 =3.44 ounces. Just multiply other percentages accordingly. Fun, huh?! A quicker, but more math intensive way is to use Bronignart’s formula, which uses the specific gravities of the slips and water to determine the amount of solid suspended in the slip. That’s coming up in part two, I have to run out to the studio to catch drying pots! Link to comment Share on other sites More sharing options...
Natania Posted July 13, 2011 Author Report Share Posted July 13, 2011 Wow. This is a great idea and something I can get my head around. Feel free to post the more math intensive way, but I am quite happy with this straightforward method. Do you think one percent a reasonable starting point for testing? I will probably calculate one percent (to start with) of whatever a dry cup of slip turns out to weigh, since my aim is to have many smallish containers of different colored slips. Thanks very much! Since you want to add frit as a percentage of the dry materials in the slip, you have a little problem, as the slip comes mixed. How to know (to a usable accuracy) how much clay has been suspended in the water to make the slip, so that you can add frit as a percentage of this dry clay? There are three ways you could do it, two of which are pretty accurate, one of which is trial and error. Accurate (but slow): 1. Weigh a measuring container in which you can accurately measure one cup of slip. (I have suggested one cup, as you say you get your slip in gallons, so I am assuming a cup measure would be most handy, rather than a metric graduated cylinder, etc.) Write this weight down, and don’t lose it!! 2. Mix your gallon of slip quite thouroughly, using the best mixing equipment you have, a drill/squirrel cage, impeller, etc. Whatever you have, use it to mix the slip very well. 3. Immediatley pour, as accurately as you can, one cup into the measuring cup. 4. Now either let the slip dry completely, either on it’s own, or accelerate the process with a hot plate, drying cabinet, warm oven, etc. You need all the water out of the sample. 5. Once the sample is completely dry, weigh the cup with the dry clay in it. Write this number down! 6. Subtract the weight of the cup alone (you wrote that down, didn’t you?) from the weight of the cup/dry clay weight. 7. The result of this procedure gives you the weight of solid material (clay plus any colorants) that is dissolved in one cup of slip. 8. Now that you know the amount of material in one cup, you can determine the total amount of dry material in the gallon of slip (or any amount of this slip, for that matter), Since there are sixteen cups in one gallon, just multiply the amount of dry material in the one cup sample you dried, and multiply by sixteen. Let’s say there is 4.3 ounces of dry material in your dried cup. (just a guess, I have no idea). 9. Multiplying 4.3 ounce by sixteen (4.3 X 16 ) gives you 68.8 ounces of clay suspended in the gallon of slip. 10. Now you can figure your percentage(s) for testing. To add one percent of frit, just multiply 68.8 by .01, giving you 0.688 ounces of frit to add to the gallon. (0.7 is close enough). To add more in percentages, just multiply 0.688 by the percentage you want. If you want five percent, you would add 0.688 X 5 =3.44 ounces. Just multiply other percentages accordingly. Fun, huh?! A quicker, but more math intensive way is to use Bronignart’s formula, which uses the specific gravities of the slips and water to determine the amount of solid suspended in the slip. That’s coming up in part two, I have to run out to the studio to catch drying pots! Link to comment Share on other sites More sharing options...
bciskepottery Posted July 13, 2011 Report Share Posted July 13, 2011 Why not phone/email the manufacturer of your prepared slip and ask them how much dry weight slip is used to make a gallon of their wet slip? Link to comment Share on other sites More sharing options...
Guest HerbNorris Posted July 13, 2011 Report Share Posted July 13, 2011 "Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime." Link to comment Share on other sites More sharing options...
Natania Posted July 14, 2011 Author Report Share Posted July 14, 2011 Also a great idea. Thanks! Why not phone/email the manufacturer of your prepared slip and ask them how much dry weight slip is used to make a gallon of their wet slip? Link to comment Share on other sites More sharing options...
Pres Posted July 17, 2011 Report Share Posted July 17, 2011 Someone recently recommended that I add a frit (3134 was suggested) to my slips to aid in adhesion/ melting when I paint them on bone-dry ware. Does anyone have an idea about what percentage would be good to start with? To complicate things I usually buy my slip wet by the gallon....? So I'm not sure how to calculate percentages this way... Thanks! Maybe not as accurate, but I used to use a hydrometer and mix the frit to the same number as the slip, then use gradiated cylinders to measure the percentage amount. I usually worked out several variations of different percentages and fired the test tiles. Many times they should shiver, or be glassy, but I could come up with a good slip/frit that was reproducible using this method. Link to comment Share on other sites More sharing options...
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