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PeterH

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Posts posted by PeterH

  1. Laser Gas Kiln Help

    in Equipment Use and Repair

    Posted · Edited by PeterH

    1 hour ago, Nick C-S said:

    I don’t know how to direct my query to Chloe (2022 dialogue with you) as you suggest. Have to hope she reads my post.

     

    Click in the icon to the left of her post, this will open up her profile.

    Click in the image.png.9fb9e0eff5963a31965c8a0e0e299c12.png icon near the top of the page.

    Compose and send a "personal message", which she will receive by email.

    With luck she will reply either by email personal message or via this thread.

    PS I believe that your email addresses aren't shared in this process..

  2. Raise firing temperature of high thermal expansion glaze

    in Clay and Glaze Chemistry

    Posted

    Three very minor comments on your last post.

    > Im hesitant to go 20% EPK again because of how thick it was last time with the FZ-16

    If people are recommending EPK for its chemistry, and you don't like its physical properties why not calcine some of it.

    >I might also try another test with my initial base recipe and 2% increments of wollastonite. However, the unwanted added silica in the wollastonite has me thinking that whiting - as bob suggested - might be preferable. Besides, the zinc and it’s late melt should give time for the calcium carb to off gas properly. Time will tell I suppose. Maybe I’ll do both. 

    Digitalfire's LOI versus temperature chart might help make this decision.
    https://digitalfire.com/picture/huctibegac
    This chart compares the decompositional gassing (Loss on Ignition) behavior of six materials as they are heated through the range 500-1700F. These materials are common in ceramic glazes, it is amazing that some can lose 40%, or even 50%, of their weight on firing. For example, 100 grams of calcium carbonate will generate 45 grams of CO2! This chart is a reminder that some late gassers overlap early melters. That is a problem. The LOI (% weight loss) of these materials can affect your glazes (causing bubbles, blisters, pinholes, crawling).

    Re microscopes, a short article by Derek Au (of glazy?) on using a macro lens on a phone
    https://www.derekau.net/blog/2018/07/12/smartphone-macro-photography

  3. US Pigments vs Mason Stains

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    2 hours ago, Morgan said:

    What’s the deal with “degussa “ inclusion stains? I cannot find any info, company info or anything about them unless I just am horrible at searching.

    Interesting.

    A search for degussa  inclusion stains found a lot of sales material, and a reference to a page on digitalfire's informative site. Which provided a partial answer
    https://digitalfire.com/glossary/ceramic+stain
    Stain product brand names can be confusing. This happens when one company buys another and continues to support the product names and numbers of the former company. As an example, the German Degussa company spun off its ceramic color business as Cerdec in 1993. They later bought Drakenfeld Colors (of Washington, PA). In 2001 Ferro USA bought Cerdec. So that means that any stain labelled as any of these three companies is actually a Ferro product now.

    So looking for evidence of this I looked for an SDS sheet, because they usually provide the manufacturers name.
    https://www.theceramicshop.com/product/14116/degussa-stain-orange-1lb/
    The Ceramic shop sells Degussa Stain, Orange 1lb, but the SDS sheet starts with
    image.png.68cebc8f0ddeb79dc28ab1f5cf508cdd.png

     

  6. Chemical analysis of clay

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    57 minutes ago, glazenerd said:

    Kelly:

    apparently I posted my Split LOI on this forum back in 2019. I would post a link, but do not have a clue on how to do that. It will give you more information without expense. 

    Tom

    I did a search for "Split LOI" in "Content tiles and body" covering "everywhere" and only got hits for two of your postings in this thread.

    ... and another for glazenerd postings in 2019  mentioning LOI (it insisted on a some text to match) again without success.

    ... a search for anything by PeterH posted in 2019 and containing "the" also failed.

    ... looks like none of my posts before 2022 are there.

    @Hulk How long are posts kept? Are there any non-active backups about?

     

    BINGO a google search for "Split LOI" test found

    So either my searches were NBG or the search function doesn't search all  postings.

  8. Poor results with Amaco Potter's Choice Blue Spark (PC-11). What can I do to improve next time?

    in Clay and Glaze Chemistry

    Posted

    52 minutes ago, Kelly in AK said:

    Check the “absorption data” from the clay seller. 

    https://www.dickblick.com/products/blick-stoneware-clay/
    Bisque fire to Cone 04 (1971°F, 1077°C). The firing range is Cone 5–10 (2205°F–2381°F). When fired at the recommended temperature of Cone 5 (2205°F), the hard, dense, semi-vitreous ware is creamy tan color with a shrinkage of 12% and absorption of 1.8%. At Cone 10 (2381°F), the very dense, vitreous ware is a soft gray color with a shrinkage of 13.2% and absorption of 0%.

  11. Another "bought an old kiln help me thread" :)

    in Equipment Use and Repair

    Posted · Edited by PeterH

    Take the gurus advice on what to do about the wiring/breaker.

    But, if their response is what I expect,  this is my understanding of why.

    >On the silver panel it says 30 amps.  On the sitter it says 45 amps. 

     I think you will find that this means
    - the kiln pulls up to 30a
    - the sitter can control a kiln pulling up to 45a

    So the load your circuit breaker will need to handle is 30a.

    But when supplying continuous loads circuit breakers may trip before their rated load.
    Information Sheet # 37 Differences Between 80% and 100%  Rated Circuit Breakers
    https://cliffordpower.com/wp-content/uploads/2020/01/IS_37_80-versus-100-rated-ATS.pdf

    Typical circuit breakers are rated at 80%, so you would need a breaker and wiring rated at 30x1.25=37.5a, i.e. a 40a one. 

    > I read on this forum a 60A circuit may be needed which is INSANE.  I HIGHLY doubt that gray 10-50 plug is rated for 50A if that.

    You  need an appropriately sized fuse in the plug to protect the kiln and its lead/plug/socket. The breaker prevents the house wiring from overheating (fire risk): hence the house wiring needs to be rated at the full breaker current, not the expected load. 

  12. Large quantities of wild clay(water processing very slow)

    in Clay and Glaze Chemistry

    Posted

    11 hours ago, Babs said:

    Lots of mudbrick building and afobe in the 60'

    +1

    Would a local historical society know about such buildings in your locality? It's where we found out about some of the older/more-unusual buildings in my area (Essex).

    Just the 1st background reading I found, so no claims about its quality.

    How to make mud bricks, and why you might want to
    https://www.heifer.org/blog/how-to-make-mud-bricks-and-why-you-might-want-to.html

    Mud brick
    https://www.yourhome.gov.au/materials/mud-brick
    ... note the mention of cement-stabilised soil bricks

  13. Raku pot liner question

    in Clay and Glaze Chemistry

    Posted

    IMHO the problems of thermal shock make this a highly "challenging" project. Not least because you will presumably be "guaranteeing" your customers that is safe to put these vases on top of their cherished woodwork.  However a couple of observations.

    What sort of raku finishes were you thinking of using? Presumably the "crackle" ones demand a certain amount of thermal shock to start the crackle before smoking, while any thermal shock involve in "reduction"  is incidental and not necessary for the final effect. Indeed thermal shock of reduction pieces might be minimised by firing them in an (open-topped?) saggar, which could be taken out of the kiln and reduction materials added to the saggar.

    OTOH the crackle finishes might stand up better the the ware-and-tear (and wetting) a vase is subject to.

    I assume a liner glaze on the inside of a pot would be less subject to thermal shock than the outside of the pot.

    I'll just mention an oddity that the raku artist Tim Andrews produced.
    Red+Raku+Tim+Andrews.jpg?format=1000w
    The glaze was a mid-fire crackle, which he fired and cooled as normal. He then re-fired/warmed the pot before taking it from the kiln and covering it with sawdust. Minimising the 2nd firing temperature, and presumably thermal shock, involved in smoking the already crackled pot.

  15. Large quantities of wild clay(water processing very slow)

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    Appendix 3 of Michael Cardew's Pioneer Potter contains a few pages on brick making with minimal facilities.

    Apparently simple bricks are made by slop-moulding using the sort of open frame Callie mentioned, although multi-brick moulds can speed things up. He suggests the slower stock-molding is used for special bricks (end-arches, side-arches,springers, bull-noses, flats, etc).

    The bricks are fired in a clamp, and the outer layer(s) of bricks are apparently discarded after firing.
    45,000 bricks give a clamp about 30ft long, 15ft wide and 12ft high - with about 5,000 (12%) of the bricks discarded.
    4,000-5,000 bricks gives a clamp about 10ft by 10ft by 8ft6in - with about 40% of the bricks discarded.

    He discusses a clamp for about 25,000 bricks with 10 fireplaces, and suggests that at least three-quarters of a cord of wood per 1,000 bricks are needed. It seems with care you can fire for 48hrs before you need to draw the embers. The firing is apparently finished when the top course of bricks glows red. I've no idea how long a total firing takes.

    PS IIRC elsewhere he discusses a bootstrap process if you want to use the bricks to make a kiln. First make a "sacrificial" kiln of  clamp-fired bricks,  and then fire another load of bricks in this kiln to a higher temperature for use in "real" kiln-building. (Assuming your cay is suitable.)

  18. HELP! Severe Shivering White Glaze

    in Clay and Glaze Chemistry

    Posted

    3 hours ago, neilestrick said:

    I agree. The kaolin, silica, and bentonite make up almost 50% of this glaze. There's just not enough fluxing going on there. I'm wondering if there was a problem with converting the recipe at some point since the numbers add up in a strange way. Maybe someone messed up the math?

    No comment on the "quality" of the glaze, just the numbers.

    Looks like a fairly direct conversion of Coleman No Craze White https://glazy.org/recipes/3331
    Custer for G-200, kaolin for EPK and silica slightly changed ... with the addition of bentonite and zircopax.

    The original recipe added up to 970 rather than 1000, which might account for funny numbers.

    PS
    Glazy seems to have the same recipe listed under Coleman No Craze White (New Zealand Halloysite) https://glazy.org/recipes/3806
    ... which claims to be Adjusted for New Zealand Halloysite.

  20. Wild earthenware question

    in Clay and Glaze Chemistry

    Posted

    Looks an interesting topic.

    Quick clay
    https://en.wikipedia.org/wiki/Quick_clay
    ... high-sodium marine clay changes is characteristics after the sodium is leached out.

    Quick clay landslides: an online documentary about Rissa
    https://blogs.agu.org/landslideblog/2020/06/18/rissa-ngi-video/
    ... showing stiff-ish "found" clay liquefying under pressure to a pourable consistency. After adding salt it it is stiff enough to hold a knife upright.

    Quick though: are you looking at the properties of the as-dug clay, or has the washing involved in the filtering removed even more sodium?

    PS If you can give us the location where you found the clay perhaps somebody can find it on a geological map.

  21. Stoneware Slip questions (UK potter)

    in Mold Making and Slip Casting

    Posted

    On 4/16/2023 at 8:34 AM, BristolPotter said:

    Every time I try to mix stoneware casting slip in the same way, I can't seem to get it past 1.6 S.G. It ends up over deflocculated if I try.

    >Yes, I'm buying in the powdered clay from Potclays, it's their 1145. I have been using way more sodium silicate (based on the recipe for casting slip from Potclays themselves), so I suspect earthenware might behave quite different to stoneware

    I'm a little confused. Looking at Potclay's site they seem to give a "starting point range" rather than an actual recipe. Can you confirm this is what you are trying to use?
    https://www.potclays.co.uk/clays-slips-grogs/clays-slips-grogs-powdered-clays/white-st-and-39;ware-powder
    https://www.potclays.co.uk/recipe-casting-slip-powdered-clay
    image.png.c7634ac6eb395eaa4269cd271da7105a.png

    As you don't have a definitive recipe I assume that you are doing small-scale experiments until you work one out.

    I assume that you started by exploring the range of recipes in Potclays recipe-range. Perhaps by a some variation on "keep slowly adding deflocculant until  you reach the sweet spot" (or more precisely until you've overshot it a bit, but can reconstruct the recipe at the sweet spot).

    image.png.6ef731e8ebeef03f2671f92b9a4d3057.png
    A rather formal version of the process is given in Determining Dispersant Additions for Casting Slips
    https://static1.squarespace.com/static/527ac372e4b0d4e47bb0e554/t/527fd7f1e4b0c046bfa9b90d/1384110065234/Dispersant+Addition+Procedures.pdf

    My guestimate based on Brongniart's formula suggest that these slips would have a SG of about 1.75 to 1.78 (see PS). So if the slip at the sweet-spot had been acceptable it would probably have met your needs. How bad was it?

    If the slip at the sweet-spot wasn't acceptable it might be worthwhile asking Potclays how you should proceed, as it makes their advice look potentially suspect.

    >Yea they are saying to use 3.5g for every 1000g of dry material but I haven't found that to get anywhere near fluid enough and I am using double that at 7g for every 1000g of dry material.

    But it's Potclays recipe advice for their clay.  If their advice has any validity surely this should be resulting in significant  overflocculation.

    Either something is badly amiss or Potclays recipe is totally misconceived.

    BTW can you confirm that your sodium silicate is 120tw and your soda ash is fresh.

     PS I note that Potclays recommend  25kg clay in 10l of water. So I'll try to work out its SG.

    Based on http://www.potteryatoldtoolijooaschool.com/brongniarts_formula_made_easy.pdf
    SG of clay is 2.5 to 2.6
    And making Brongniart's assumption that the solids don't dissolve, but simply occupy their volume in the final slip ...

    Weight of slip = weight-of-clay + weight-of-water = 25kg + 10kg = 35kg
    Volume of slip = volume of clay + volume-of-water ...  between 10 + 25/2.6 and 10 + 25/2.5 litres = 19.6 to 20

    So SG of Potclay's slip is weight/volume = 1.75 to 1.78

     

     

  25. Microwaved Wedding band

    in Studio Operations and Making Work

    Posted · Edited by PeterH

    A hybrid technology: stainless steel ring with inlay (here polymer clay).

    Video using Fimo Soft (maybe not the best polymer for jewellery)

    One source for suitable stainless steel "inlay" rings
    https://www.amazon.co.uk/dp/B09N6XQ1LG/ref=twister_B091KYY4B1?_encoding=UTF8&psc=1
    image.png.e3f63a8deb7d977d8f711608a6a04f0a.png
    image.png.9578ed146d453f36780e27e72d5d11df.png

    PS This may be relevant
    Best Polymer Clay for Earrings and Jewellery
    https://sarahmaker.com/best-polymer-clay-for-earrings-and-jewelry/

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