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Min

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Posts posted by Min

  1. +1 for leaving the liner glaze dry before glazing the outside. Most of the time I have a different glaze inside my mugs than the outside one. I pour and dump the liner glaze then for the ones where I want a clean line, or where the two glazes can crawl if double dipped, I use a water based wax resist over the glaze. When that has set up I wipe the excess glaze above the wax. I try and do this at the end of day one. I leave the mugs dry overnight then glaze the outside on day two.

    Even for the mugs/tumblers that don't need the wax resist line I leave the liner glaze dry overnight, I find that with my glazes it makes for a more even glaze laydown of the exterior glaze. Other thing that can happen is as the moisture from the exterior glaze gets soaked into the bisque it can re-wet the liner glaze. This is fine if the liner glaze is dry but if it's still damp it can loosen the bond of the liner, for thicker walled pieces this isn't usually an issue but for thin walled pieces it can be. Leaving the glaze dry overnight helps prevents this happening too.

  2. 7 hours ago, GEP said:

    The other is requiring masks and proof of vaccination. It turns out the “proof of vaccination” is to show our vaccination card, and a photo or photocopy is good enough. Not hard, and probably easy to fake but I don’t think the demographic that attends craft shows overlaps with the demographic that is faking vaccine cards.

    I find this really surprising; your state leaving it up to event planners to decide what constitutes "proof of vaccination". 

    I'm not saying things are working better here in BC but we have to show a QR code that is issued by the province on our phone (or a printed copy of it) when entering a non essential business, indoor sporting event or care home. Person at the door(s) for those places has a QR code reader that they scan our phone QR code with plus we need to show government id to verify we are the same person as what's on our QR code. All indoor spaces require masks for people 5 and older. We are at just over 70% of elegible people being fully vaccinated, for now thats 12 and older, soon to be 5 and older.

  3. Perhaps the kids work is made from low fire clay and she had you using cone 6 clay. It is quite common to use lowfire clay for kids work. It could just be that she doesn't know if the underglazes will work at cone 6 and / or she doesn't have a cone 6 clear glaze to use over top of them. 

    I would go back to her and ask if you could at least try the underglazes and have your work fired with the kids work. If you have cone 6 clay it will be underfired at lowfire (if that is indeed what she fires the kids work to) but if you are only making decorative work it would be better than nothing.

    I agree with the others who said if possible find another place to work out of. 

  4. Just to clarify, your glaze isn't hard panning / settling out but is now "thinner" than you would like it to be, and at 1.46 SG you get a thick enough glaze layer. If that's the case and you have been unsuccessful with adding more saturated epsom salts solution then I would try something else.

    Some glazes respond better to vinegar than epsom salts. I would suggest removing a cup or so of glaze from your bucket and stirring in a few drops of vinegar, give it a stir and see if that does the trick. Dip a test tile and see if you like how it goes on. If it works then go on to adjust the bucket of glaze. Over time you might need to add more vinegar if you find the glaze deflocculates. 

    If that doesn't get the glaze as creamy thick as you would like (while maintaining the SG) you could give MAGMA a try. This product will work really well to both flocculate and increase the glaze thickness. Word of warning about it though, side effect it has is to slow down the drying time of the glaze so there is a balance between slurry thickness and dry time. Once Magma is added you won't need to add more, it doesn't loose its effectiveness overtime. Do add the 0.04% copper carb if it's going in a glaze without copper as it will spoil / rot if not used up quickly.

  5. 15 hours ago, Ann E. V. said:

    I did have another large piece  with the same issue that I refired to cone 6 and the stroke and coats tried to crawl off the piece.

    This sounds like an application issue as Stroke and Coat can go to cone 6. Perhaps dusty or oily bisque or thick a glaze layer or coats not dry between layers.

    15 hours ago, Ann E. V. said:

    I applied them when the sculpture was firm leatherhard and should have probably applied them when the clay was more moist? 

    Yes, get the slip on there as soon as you possibly can. To reduce the water content in the slip you can add a tiny amount of darvan to an overly thick slip to "thin" the slip to brushing consistency. You might want to consider adding zircopax to your slip to skip the white underglaze. Again, test tiles are your friends.

  6. 52 minutes ago, Bill Kielb said:

    Not sure that is the best representation of the kiln in actual use, especially if  it’s unable to maintain a reasonable final rate.

    That's the beauty of the controllers, with a cone set for the peak (not a set temperature) the controller takes the rate of climb into account and adjusts the final temp accordingly. 

     

  7. 2 hours ago, Bill Kielb said:

    Hmm, ……….how would one calibrate by using cones in a single TC kiln?

    Shelf/shelves  and a cone pack in proximity to the new tc, same as for a loaded firing with a controller and programmed for a cone firing, not a peak temperature. If the aim is to test the tc with the fall of a cone it seems logical that load wouldn’t factor into it. We don't reprogram a cone firing differently for a light versus heavy load, controller adjusts heatwork to reach the target cone.

  8. @bryandave, are those two different claybodies? Seems the crazing is worse on one than the other.

    20 hours ago, Bill Kielb said:
    • calcined kaolin  - 26.79
    • 3124      - 25.00
    • silica   9 -> 19. = matte -> Gloss..
    • dolomite -  8
    • talc  - 12
    • wollastonite - 4
    • neph sy. - 20

    I would suggest not using all calcined kaolin if you try Bills recipe, I'ld go with around 20 kaolin and the remaining calcined (balance it to allow for the loi). I have a hunch this is going to craze also, I think there is going to be too much high expansion sodium in the formula. I like the increase in boron and silica though.

    Revisiting your last recipe, I think the silica is too low (for a durable glaze), the sodium and potassium too high (contributing to crazing on your clay) and the boron too low for a good melt at cone 6. I think there are a couple ways to attack this glaze if you want to put the time into tests. First off reduce the high expansion fluxes (sodium and potassium). Replace those with low expansion fluxes, more magnesium and or lithium. Lithium supplied from spodumene or lithium carb, problem with this is lithium can effect the melt so you might loose some of the matte quality of the glaze. It also needs more silica which is going to throw the silica to alumina ratio off so that would need adjusting. How much silica and alumina can be taken into a melt is going to be trial and error. It might be okay with more silica but I think the craze lines are too close together on that one glaze sample you posted for this to work.

    Going back to Neil's suggestion of trying a different glaze recipe, I use a version of this glaze blended with my low expansion clear to make a good semi matte that doesn't craze on my low expansion clay. If you can get Ferro Frit 3249 where you live the other version of that glaze has a bit better a melt. If you have a clear that fits your claybody I would give it a try, blend your clear with the matte base to fine tune the amount of matteness. To make it white add tin or zircopax. I haven't found a durable fully matte glaze that withstands cutlery marking, I don't know if you need this glaze for food surfaces but having a semi matte/gloss resists cutlery marking better than a matte.

     

  9. Crazing from a too great a glaze vs clay coefficient of expansion issue like Bill said, I would fire some test tiles hotter and see if that helps, if not then you will need to change either the claybody or the glazes to ones that "fit" together without crazing.  Since you are using commercial glazes this is going to be a trial and error process.

    I'm wondering if the shivering is due to a poor bond between the slip you brushed on  and the piece. How dry was the piece when you brushed on the slip? Fairly thin slip or ? Also, when the glaze lifts off is it taking the underglaze with it? It's uncommon to have both crazing and shivering with the same glazes / clay.

    Going forward I really strongly suggest doing some small test tiles / scrap pieces to test with. Include some corner angles and edges with the slip & underglaze and glaze as shivering often occurs in those areas. Tap the edges / corners with something like a knife handle, if there is a loose bond it should shiver off then if it's going to.

     

  10. This could just be someone got their wires crossed, (yup, bad pun intended). Skutt video on replacing a TC says at the end to perform a test fire with an empty kiln to make sure the TC is working properly. The written blurb says basically the same thing using cones to verify in an empty kiln.

  11. 59 minutes ago, laughlin said:

    Hmm - if those can be smudged with a finger that might work, on bisqued  underglaze.

    Amaco Underglaze chalk crayons do smudge really well. There is a blush rose colour, maybe that tempered with some of the light brown or white would work. They are fragile so maybe crushing a little bit of them to a powder then using a makeup blush brush to apply then work into the bisque would be worth trying.

    1845004618_ScreenShot2021-10-08at11_56_10AM.png.640af3ff4c902042952ce6fc671417a7.png

  12. Hi Jasmine and welcome to the forum.

    Lustres are an overglaze so it's best not to use your Hanovia Opal on bisque. I would suggest using a gloss glaze on it first then applying your lustre and firing to the recommended cone, gold lustres are usually fired to cone 018 and mother of pearl lusters to cone 020. Lustres take on the finish of the underlying glaze so a matte glaze will give a matte result, gloss will give gloss. You really need to work outdoors if possible and if not then work in a really well ventilated space, either way you also must wear a respirator rated for vapours not just dusts. For firing, load the kiln loosely and keep it well ventilated, just your regular glaze firing should be fine but obviously you will be firing much much cooler. (That zero at the front of the cone 018 is important!)

  13. 21 hours ago, docweathers said:

    There are some very small fine cracks.

     

    1 hour ago, docweathers said:

    3. There are no cracks whatsoever in the glass.

    You lost me here. 

    I believe people are just trying to point out the risk you are taking of both  glass splinters coming off the bowls and the probable toxicity of some of the glass. If that orange is melted glass I would add cadmium sulfide and selenium to the ones Callie mentioned.

  14. Plaster batts are wonderful for large wide pots, no wiring off needed. Economical to make yourself from #1 Pottery Plaster and springform cake tins from a thrift store. They can be attached to the wheelhead with a clay donut or a BatMate, if you want to use pins they can also be made to accommodate those but it's more work / fuss.

  15. For pots around 4-5" or so at the base you can use a wide paint scraper to slide under the pot after it has been wired off.  Dip the paint scraper it water then push it under the pot and lift it off then put it onto a ware board while pulling away the paint scraper. Another way to do it is to use a piece of thin paper (newsprint or pages from an old phone directory) on the rim, gently run your finger around the rim on top of the paper. Wire the pot off then pick it up as close to the bottom of the pot as possible. Place it on a ware board then remove the paper. This can mess up the rim a bit but just leave it alone until it has firmed up a bit then smooth out any blemishes. Rib off the outside of your pot and dry your hands before taking the pot off the wheel.

    Another approach is to purposely make the rim out of round.

    Best solution might be to get some better batts for your wide pots.

  16. @Bill Kielb, problem with subtracting the weight of the water from the weight of the glaze slurry to calculate the amount of solids in the slurry is it doesn't take into account the specific gravity of the solids in the glaze slurry.  SG of water being 1 whereas the SG of typical glaze materials are typically averaged out to 2.5 or 2.6   For 100ml size sample the difference might not seem huge but multiply that out for a 10kg / 5 gallon bucket of glaze and it would be.  Brongniart factored the SG of glaze materials into the equation.

  17. If you go by the general glaze mixing directions that Peter linked the ballpark figure of 9.5 fluid oz of water to 1 pound of glaze might be too little water. When I used this glaze it was more like a 1:1 ratio. @Karen Rycheck, could you measure the specific gravity of your glaze slop? From this link it should be between 1.42 and 1.45 for dipping, if we can determine that then it's more likely you have the 1:1 ratio of glaze to water rather than the ballpark amount of a 1 to 0.6 ratio from Peters link. If the specific gravity is a fair bit higher it would indicate more along the lines of Peters figures. Would make a difference to the amount of stain needed. 

    If all else fails there is always the Brongniart formula .

    Welcome to the forum.

  18. It's hard, if not impossible, to mix dry bentonite into soft clay directly. I'ld suggest drying out a 1/2 kilo or so of it. It will take some testing to see how much bentonite is needed, ballpark around 2% should give you an idea of how much is needed. So if you want to test 500 grams of clay use 10 grams of bentonite. Slake the bentonite down in water, just sprinkle it onto around 200 mls of water then don't touch it, just leave it to slake for a few hours and  has settled to the bottom of the water. Break up the clay as best you can so it's not one solid lump then add water to your dry clay and slake it down to make a thick slurry then add  the slaked bentonite and mix it up really well, use enough water to be able to stir up the clay. Dry out the clay to a workable consistency and see if the 2% was enough. 

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