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PeterH

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Posts posted by PeterH

  1. Asking for a friend: underglaze question

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    Some previous thoughts below.

    Especially @neilestrick
    I agree that the organic binders/extenders are diminishing. Typically they put a biocide in there to preserve them, but if they are especially old it can wear out. Add some gum solution with a touch of copper carb in it to preserve it. I usually make gum solution 2 tbsp bum to a gallon of water, plus 1/8 teaspoon copper carb.

    As your friend's underglaze seems to be having  a shortish life before thinning is there any special source of contamination/warmth that might be causing this? Are they using large bottles, and might decanting a working-stock into a smaller bottle help? (And maybe keeping the large bottles in a cooler location.)

     

  3. Duncan kiln box repair

    in Equipment Use and Repair

    Posted

    8 hours ago, Alex147 said:

    And does anyone have the wiring diagram for the control cables? 

    What country are you located in?

    What model is your Duncan?

    If it's any help here is a wiring diagram for the Skutt KM-1
    https://skutt.com/pdf/service_manual/12-7_km-1.pdf
    The only connections to the kiln seem to be a mains socket on the KM-1 and a thermocouple.

    ... there is a description at
    https://skutt.com/ceramic-kilns/kiln-accessories/km-1-wall-mounted-controller/

  7. Cobalt carbonate majolica technique troubleshooting

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    36 minutes ago, Hundy said:

    Thank you for the advice. You did a great job of explaining and it's a good thread that one. I definitely feel like I know nothing with the variety of things I've unearthed as just an addition to the cobalt like frit, flux, clay, glaze, medium, gum arabica, green tea, gerstley borate(sounds like a train station here), elmers glue etc etc. I mean it really feels like alchemy. 

    I've also read of "flat" seven-up as an alternative to green tea as a solvent/vehicle. I suppose that the sugar acts as a binder as the "ink" dries.

  8. Glaze Disappeared during firing

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    16 hours ago, lanniec said:

    All painted the same. Same number of coats, painted at the same time. The other two that the glaze/underglaze vanished were the same as the two glazed in the photo.

    A weird glaze result is one thing, but it's really hard to believe that an under-glaze could completely disappear on firing. Let alone four different under-glazes: red, orange, black & light green.

    Sorry, but to err is human.

  9. Gold Lustre

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    @Imu Just found a very old jar in the garage labelled

    Bismuth wash
    100 water
    25 Bismuth Subnitrate
    18 Citric acid

    Not a published recipe, but something I knocked together to increase solubility/dispersion. Probably for a raku party.

  12. emergency MATH problem!

    in Clay and Glaze Chemistry

    Posted · Edited by PeterH

    @oldlady  In case it's of any use I've reformulated your problem as an exercise in form-filling. I hope that it breaks things down so that each step seems like a logical progression.

    The idea is to look at what you have done so far and calculate a NewRecipe which is a scaled copy of the original recipe which is:
    - large enough to accept all the ingredients already in your bucket
    - and at least the size of the original recipe
    ... and then calculate the AdditionsNeeded to the bucket to match the NewRecipe.

    As you didn't list your full recipe I've tried to reconstruct it (as a 10,000 gram batch with a 2% addition of bentonite). So check I've got things right.

    Here is the form. which is filled in column by column. Note that BatchSize is the largest number in the MinBatchSize column (or 1, whichever is greater).

    GlazeProblem_cropped.jpg.aa86d4ab675be3bab77aad5b2eac72a8.jpg

    PS This seems to give the same results that Min has already posted.

  13. Thermocouple offset vs lowering max temperature

    in Equipment Use and Repair

    Posted · Edited by PeterH

    Just for the record a cone 6 controlled cooling cycle for glaze development is given in
    https://ceramicartsnetwork.org/daily/article/Super-Cool-Slow-Cooling-in-an-Electric-Kiln
    Natural cooling down to 1900 F(the poster seemed to get 500F/hr but programmed 9999F/hr)
    125-175F/hr down to 1450F (tweak based on glaze results)
    Natural cooling down to room temperature
     

  15. Any tutorials on this "stencil + rolling pin" technique?

    in Studio Operations and Making Work

    Posted · Edited by PeterH

    16 hours ago, pojkoo said:

    I really like works of Gabrielle Renoir (https://www.instagram.com/gabriellelenoir/?hl=ru), she does this inprinting on clay by pushing stencils with a rolling pin. I try to do the same and it doesn't look so nice - I don't get such even edges and it's hard to put out the paper without damaging the surface. Maybe my clay is too wet. I see that they are a lot of nuances.

    I wonder if a more water resistant/repellent material would help. (Like both of Min's suggestions.)

    Materials used in stenciling might also work, and translucency/transparency could help when cutting out the patterns. But that would probably mean art-shop prices.
    https://ceramicartsnetwork.org/pottery-making-illustrated/pottery-making-illustrated-article/Stenciling-on-Clay#
    Stenciling on Clay

    PS A recent article on stencils which are very finely cut. Shows just how far people can push things.
    https://ceramicartsnetwork.org/daily/article/how-to-use-vinyl-stencils-and-underglaze-for-beautiful-surfaces
    How to Use Vinyl Stencils and Underglaze for Beautiful Surfaces
    claycanvas-duvall-12-0924pmi.jpg?sfvrsn=

  16. emergency MATH problem!

    in Clay and Glaze Chemistry

    Posted

    Idle thoughts.

    10 hours ago, Russ said:

    Oh by the way I never make ANY mistakes!:rolleyes:

    This may be the best way of avoiding the maths! (Besides asking your very willing friends to help.)

    The problem seems to be restarting the mixing after an interruption (a phone call in this case).

    Maybe after an interruption it's worth taking the time to:
    - Write the recipe down on a scrap sheet of paper
    - Tick off the ingredients you have already added
    - Add the extra ingredients, ticking as you go.

  18. Best Clay for Making a Dutch Oven or Bread Baking Cloche

    in Studio Operations and Making Work

    Posted

    1 hour ago, TonyC said:

    I need to read more about the proper pre-heating of the cloche and what that might do to the bread. 

    Pre-heating from cold seems to be recommended practice. Don't know how severe the thermal shock is when you place the bread into the cloche.
    https://delbuonosbakery.com/mastering-bread-baking-with-a-cloche-a-comprehensive-guide/
    Cloche Preparation: Begin by placing your bread baking cloche, both the base and the lid, in a cold oven. It’s essential to allow the cloche to heat gradually with the oven to prevent thermal shock, which can damage the stoneware or earthenware.
    ... obviously only put the hot cloche down on an insulating surface, such as wood.

    Interesting to see how nicely rounded the the transition from base to wall is. Probably because the resultant alignment of the clay particles minimizes the chances of type H cracks when it's thermally shocked.
    https://ceramicsfieldguide.org/pdf/materials-handouts/ClayCracks.pdf

    PS The subject of pizza stones comes up from time to time. Kiln shelves are often recommended - as a body less subject to thermal shock. So should you ever need a flat baking stone ...

     

  22. Sentry 3.0 SFTY setting

    in Equipment Use and Repair

    Posted

    I just used my very old analogue ammeter to read the mains voltage in my UK house. I got 245V +/- 5%.

    My equally old digital meter (accuracy unknown) oscillated between readings of 239V & 240V.

    @davelea As Neil said measure your voltage. If your house is really receiving 240ish volts then I think there may be valid concerns running a kiln with elements designed for a 230v supply.  But the experts are much better judges of that than I am. 

    BTW if your supply is 240V changing the elements to ones designed for 240V looks like a complete fix. The question then is does this need to be ASAP, or can you just wait until the elements need changing? I'm leaving that to the experts. The fact that you will be running hotter once the controller lets you may be significant.

    PS

    8 hours ago, Bill Kielb said:

    Very likely the EU and Uk standards have evolved similarly for a best compromise.

    For the record I think that the "nominally 230v"  was a good idea technically. It  helped create a unified market for (most) electrical goods in Europe (not just mainland Europe). The downside was that it introduced a certain amount of bureaucratic double-speak, whose impact seems to have worsened over the years.

    At the stroke of a pen the nominal 220v European supply became nominally 230v, and the UK nominally 240v supply became nominally 230v. While as intended  the actual voltages supplied didn't change at all. (Although there could have been longer term changes in these voltages as the electricity grids changed over time).

    Looking at wiki https://en.wikipedia.org/wiki/Mains_electricity_by_country
    France and Germany are listed at an unqualified 230V, although the legislation said 230V -10% +6% (i.e. 207.0 V-243.8 V). The UK is also listed as 230V, although a footnote leads to an article that states that the range is really 230V +10% - 6% (i.e. 216-253v or 234.5V +/- 18.5V). 

  25. Sentry 3.0 SFTY setting

    in Equipment Use and Repair

    Posted · Edited by PeterH

    1 hour ago, neilestrick said:

    Then everything on the serial plate is correct, and the kiln should function perfectly fine once you get the controller peak temp sorted.

    Well not quite -- as the UK supply is nominally 240V not 230V.

    Since WW2 most of continental Europe has used a 220V supply, while the UK used 240V.

    Come European “harmonised voltage limits” they showed "neither fear nor favour of the two sides" and defined things in terms of 230V.
    https://leadsdirect.co.uk/knowledge-base/what-is-the-difference-between-uk-voltage-and-european-voltage/
    So: 
    - The UK's nominal 240V became the range 230V -6% +10% (i.e. 216.2 V – 253.0 V)
    - Europe's nominal 220V became the range 230V -10% +6% (i.e. 207.0 V-243.8 V)
    - This effectively means there is no real change of supply voltage, only a change in the “label”, with no incentive for electricity supply companies to actually change the supply voltage.

    So the UK supply voltage remains nominally 240V.
    ... and the same kiln draws about 4.3% more current and about 8.9% more power than it would from a nominally 230V supply.

    PS
    Equipment designed to operate correctly of a voltage range 230V +/- 10% can operate on either of there standards, and most goods on the market are moving towards this.

    BUT this isn't possible for simple heating devices.
    - Europeans don't want their fan heaters to run 9% cooler than UK ones!
    - A 9% hotter incandescent bulb runs brighter, but has a significantly short lifespan. (I found out the hard way).
    - Kilns!

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