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Bam2015

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Posts posted by Bam2015

  1. Crazing question

    in Clay and Glaze Chemistry

    Posted

    Min, thank you for your thoughtful response, great info to have. I am going to start mixing & testing my own clears and have Britt's book, so I will start there. I am just starting to understand the chemistry behind this. Over the past year I have spent my time focusing on throwing skills. I see that I need to expand my knowledge and learn about glaze fits. 

    Betty

  2. Crazing question

    in Clay and Glaze Chemistry

    Posted

    Hi All,

    I said I would share the clear glaze recipe when I got it. Here it is from the studio who mixed it for me. 

    EP Kaolin                 20.00

    Ferro Frit 3134    20.00

    G-200 Feldspar    20.00

    Silica                            19.00

    Wollastonite           15.00

    Talc                                   6.00

    It's also on this website. 

    https://glazy.org/recipes/6798

    Any thoughts on how to adjust this recipe to reduce crazing is appreciated. 

    Betty

  4. Crazing question

    in Clay and Glaze Chemistry

    Posted

    Thank you Min. I will heed your advice and appreciate you taking the time to thoughtfully respond to my post.

    I asked the studio if they would share their recipe and if they do, I'll post it, otherwise I will start from scratch with some of John Britt's recipes. 

    Betty

  5. Crazing question

    in Clay and Glaze Chemistry

    Posted

    Min, I am going to ask them for the recipe and if they provide it, I'll share. I doubt it's a recipe that they developed on their own.

    Although I pulled out some pieces that I previously fired which crazed, I also have several pieces from when I first bought the glaze that did not craze. So maybe it just needed to be thinned? I'll do some testing now that I have thinned it a bit. 

  7. Crazing question

    in Clay and Glaze Chemistry

    Posted

    Min & Dick, thank you for your responses. Yes,Orton  witness cones on each shelf. The cones indicated proper firing.

    Dick, I just measured the SG using the method you indicated. I read a number of articles against using a hydrometer. The SG  was a bit high, so I added water. I'll see if that helped. 

    Oh well, what a bummer! Was hoping for an easy fix and maybe thinning it will help.

    I guess I should I just start mixing my own glaze(s)? I just want a clear glaze, I use a lot of underglazes and mason stains.  

    Just when you think you finally have things figure out. :) 

  8. Crazing question

    in Clay and Glaze Chemistry

    Posted · Edited by Bam2015

    Morning All!

    I know that crazing has been covered in a number of threads, but not sure the questions I am about to ask have been addressed. I have been using the same clear glaze with success for several kiln loads on both Laguna #15 cone 6 porcelain and Laguna #65 stoneware clay with success (no crazing), but this last load crazed, both the porcelain and stoneware. I did not mix the glaze, I purchased it from a pottery studio where I used to be a member, they mixed up a batch for me. 

    I'm wondering if the following can help to reduce the risk of crazing:

    1) Thin the glaze a little with water? I don't have any glaze making chemicals to add to fix this problem nor do I own a hydrometer, but I could buy one. 

    2) Does glazing the inside of the pot and not glazing the outside reduce risk of glazing?

    3) Does bisque temp/cone make a difference? 

    I think I had one more thought, but it's left my brain. Thank you in advance.

    To those forum members in Ian's path I hope you're ok.

    I just edited my post because I first said that I don't want to mix my own clear glaze, but if that's the answer then why not? 

    Betty

  11. Underglaze question please

    in Clay and Glaze Chemistry

    Posted · Edited by Bam2015

    Hi All,

    As I was painting underglaze on greenware pots today, I started thinking about how underglaze affects pottery seams like mug handles.

    So here is my question, does underglaze have a negative, positive, or no affect on greenware pottery seams/joints? In other words, does added moisture from the underglaze affect drying and potentially cause the seam to open up? Or does it help to seal a seam? Or maybe the affect is neutral.

    I know that one or more of  you know the answer. :)  

    Thank you,

    Betty

  13. Kiln question

    in Equipment Use and Repair

    Posted

    Thanks Neil. That's what I assumed but last time I did a glaze fire, most of my little porcelain bowls cracked on the bottom and I had shut my kiln switch off after the firing was complete. So I was wondering if I made the kiln cool too quickly and that caused the cracks. I've used porcelain in the past without this problem.

    This time I dried them pretty quickly, I treated them like stoneware, so maybe that was the problem. 

    Betty

  16. Slab Roller Issue

    in Equipment Use and Repair

    Posted

    GLR, what do you have the roller set on with your first pass through and then how much do you change the setting? I'm asking because I find that if I don't make multiple pass throughs and only change the setting slightly then the  clay then it sometimes buckles on itself and cracks. I hope that made sense. I also change the orientation of the clay each time I pass it through the rollers. 

    Betty

  17. Did I make a mistake? What do you think will happen?

    in Clay and Glaze Chemistry

    Posted

    1 hour ago, Min said:

    From this I would assume you are using an underglaze that contains CMC?

    But then, from the quote below it sounds like it could have been CMC + stains?

    Could you clarify what you used that had the glaze resist some areas as CMC + stain doesn't equal an underglaze.

    Min,  I brushed the outside of the pots in underglaze (no CMC mixed in). I then added designs using stencils. In the stenciled areas I used Mason stains mixed with CMC. I used the CMC thicken the Mason stain mix so it would be less likely to seep under the edges of the stencils. 

    I hope that made sense. Sorry if I confused anyone.

    Betty

  20. Did I make a mistake? What do you think will happen?

    in Clay and Glaze Chemistry

    Posted

    14 hours ago, neilestrick said:

    Some underglazes don't take dipping glazes very well unless you bisque fire them before glazing. Speedball underglazes are like that. If it looked like your glaze covered well when you applied it, then things will be fine unless you fired too fast for your clay and glazes liking. The problem is that if you go too fast, the glaze starts to melt before there has been sufficient time for the organics to burn out of the clay, and those gasses can get trapped in the clay and cause bubbling.

    Neil, thank you for chiming in. Your responses are always spot on. 

    Old Lady, I will share results. 

  24. Did I make a mistake? What do you think will happen?

    in Clay and Glaze Chemistry

    Posted · Edited by Bam2015

    I was loading a glaze kiln and because I still had some room, I decided that I would single fire a couple bowls. I've never single fired.

    My concern is that I used an underglaze with CMC in it and then dipped them in a clear glaze. Just small areas of underglaze with CMC. I was using stencils and wanted the underglaze to stay put.

    Was it wrong to put glaze on top of an underglaze with CMC and then just single fire? Should I just fire and see what happens? What could happen? I plan to fire to cone 6.

    Thank you,

    Betty

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