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Min
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Posts posted by Min
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I'll try and find my glaze book from back when I did crawl / reticulation glazes, maybe one of them will look familiar to you.
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Looks like the solubility of anhydrous borax in room temp water is 2.7 g/100 ml vs borax at 6.3 g/100ml so it's about half as soluble. Couldn't find solubility numbers for frits to compare with.
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Heads up for anyone using Laguna commercial glazes, some of their glazes are being discontinued in small amounts. 50lbs and or 5 gallon sizes available on special order once existing inventory is gone.
List of glazes going to special order only here: https://www.lagunaclay.com/_files/ugd/e5330f_47a0a60e5af84df38d03d1d5b02c3056.pdf
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Post a picture of the damage, might help with getting an answer.
welcome to the forum.
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Hi Karen and welcome to the forum!
How old was the plaster you used and how was it stored?
edit: link from USG on weighing and mixing plaster here.
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20 hours ago, njabeid said:
5) I wonder why the interiors pinholes so badly. Need to make the surface smoother.
My hunch would be that given there is less air circulation inside the pots during the bisque firing less of the problem materials in the clay had a chance to off-gas.
Looks like these mug tests are more successful than the previous ones. Local white clay + opacifier on damp clay seems the most successful of the lot with slip only on the outside better than the ones with slip inside. Is that about right? How much opacifier did you add to the slip?
20 hours ago, njabeid said:It almost melted pathetically to a puddle, handle cracked, but the result the front cup in the picture is better than all the others, which were brushed with a hake brush
If you had a thicker slip laydown with the dipped slip mug then my takeaway from this would be to either dip when the mugs are still damp or deflocculate the slip and brush it on the damp pots.
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For drying flat slab pots I always weigh down the center of the pot to avoid it rising up as the edges dry faster than the inside. I usually use a square or triangular kiln post on its side, with really large slabs I put the kiln post on a batt to distribute the weight. I keep the weight on (especially after Christmas,
) until the pot is bone dry. I keep slab pots right side up.
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Like has already been said the physicality of working with clay has its draw, for me it’s with both hand building and throwing, but another huge pull is in the number of “why’s” that are involved with working with clay.
Seems the more I learn the more paths or rabbit holes open up, there is just so much to explore, learn and puzzle through.
As to the QOTW, if I had to label myself with a personality type I would have to say inquisitive is probably pretty accurate. As to actually working with the clay itself I know that if I've got something stressful going on it won't be a good day to throw.
- Hulk, Magnolia Mud Research, kswan and 2 others
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@maz, thanks for sharing your experience with it. Let us know how your re-fire goes.
Welcome to the forum
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@PeterH, I believe the formula for sodium to work as a defloc is it needs to combine with calcium as in the following equation, Na2CO3 + Ca2+ = CaCO3 + 2Na.
Simple enough to test sodium bicarb out as a clay slip defloc but I don't think it will work.
@Babs, for sure your schedule could work too. It's getting more and more expensive making pots with costs for just about everything going up isn't it?
edit: adding a link to a Britt video showing what sodium silicate does to a slip and how you would then add more dry clay to make a more "concentrated" slip. ie one having the same amount of water but more clay. Video also shows how to use epsom salts to do the opposite and flocculate a slip.
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2 hours ago, njabeid said:
- @80 to 700, then @60 to 1000, total 13:40 hrs, (soak at the end?)
- @80 to 700, then @50 to 1000, total 14:40 hrs, or
- @80 to 800, hold 1 hr (?), @80 to 1000, total 13 hrs or more with a longer soak
which do you think would be best?
maybe I should also modify my glaze firing schedule to slow it at the end? Now it is …
I just went to check and discovered there are actually 3segments! ( modify the above schedules?)
@80 to 90, 1 hour hold, @180 to 600, @120 to 1100, 20’ hold.
Should I take the @180 up to 900 then slow right down?
The schedule I linked above includes a 12 hour candle (low temp soak), if your pots are dry you don't need this. If you aren't sure pots are bone dry then to cut down on the length of time the kiln is running heat it up to 90C in the evening the day before you are going to fire then soak it for X amount of time, an hour should be plenty based on what you are making and where you live. Turn the kiln off after the soak and leave it until the morning. Residual heat should dry everything out just fine. This leaves you back up to 3 ramps for your bisque firing.
Perhaps something along the lines of
Overnight as above then in the morning 1) 110C to 700C no soak. 2) 50C to 900C no soak. 3) 42C to 1000C no soak.
If you try this please don't try it with anything precious until you test it out.
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1 hour ago, njabeid said:
I bisque fire @80°C to 600 then 120°C to 1000°C. How slow or fast is that?
So I'm going to assume there is some, maybe a lot, of stuff in your clay that probably needs burning out which hasn't been with your existing bisque schedule.
There are a couple temperature zones that carbons (both organic and inorganic) burn off plus there is also sulphur. Given that you have a maximum of 2 ramps (with holds) I would suggest that firing your bisque slowly through the 700C - 900C would be where I would try. Given that you end your bisque at 1000C I would slow down from 700C thru to 1000C. This would be your second ramp.
I don't know what the cost of electricity is in your area but I do recall you saying you have frequent power outages so it's going to be a balance between cost + liklihood a power outage verus the ideal rate for the crap to burn out of the clay. Have a look at this ramp schedule for really problem claybodies and adapt it to your circumstances and 2 ramp controller. If you can drop down to 40-50C / hr from 700C to finish I would try that. Other option would be to not slow it down that much but add a hold at around 800C.
Re soda ash vs sodium bicarbonate, snippet below from Laguna Clay via Marjon Ceramics:
- "SODA ASH Soda ash works with sodium silicate to aid in deflocculating. The correct combination of the two will give proper casting qualities. Soda ash works to dissolve lignite in clay. It works as a deflocculant, but if only soda ash is used as a deflocculant, your clay will become sticky. If soca ash is not stored in tightly closed containers, a chemical change occurs and it becomes sodium bicarbonate (baking soda). If this occurs it will then act as a flocculant (it will thicken) instead of as a deflocculant."
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2 hours ago, Jeff Longtin said:
Tin Violet is a really intense purple but owing to the tin its terribly expensive. You could also try Pansy Purple.
Cd inclusion stain Violet from US Pigments is running at $30 a pound, might be another option. It's about half the price of Mason's 6304 Tin Violet.
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5 hours ago, njabeid said:
...on one hand they might arrive in June 2024
I am never ever going to complain about the time it takes me to pick up supplies!
On 12/29/2022 at 7:07 AM, njabeid said:...but any addition of copper oxide (2%) or cobalt carbonate (0.3 - 0.5%) - or for that matter any other glaze with those oxides in - results in disaster: crawling, pinholes, and some odd holes that look as if something blew up under the engobe, folding out the engobe+glaze.
Misinterpreted what you wrote in your first post snippet above, thought there might be an issue with your cobalt and or copper but you've cleared that possibility up.
2 hours ago, njabeid said:My bisque firing schedule rises at 80°C up to 600 and then 120 up to 1000°C. My controller is very limited. Should I go even slower? Or just add a soak?
In an ideal world you would slow it down during specific temp ranges. Is your controller limited to 2 ramps?
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@grackle, what's really important to get consistent results is to measure the specific gravity (sg) of the glaze. X seconds in a watery glaze slurry won't give the pots the same coverage as the same number of seconds in a thick glaze slurry.
Specific gravity measure the glazes density in relation to that of water. Just in case you aren't doing this already a link here on how to quickly measure sg. with a syringe if you need it.
Generally speaking the less porous the clay (from hotter bisque firing) the higher the sg could be if the number of seconds the pot is being dipped remains constant. SG is the third variable in the process. If the sg remains the same but a clay is bisqued hotter then the X number of seconds a pot is dipped could well need to be increased.
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Interesting approach, makes a lot of sense to do it like this. Slip casting seems the perfect vehicle.
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5 hours ago, njabeid said:
although as you say the slip goes transparent and I find it hard to get an even coat, even with a soft hake brush; as you can see in the bowl.
Have you tried making this slip whiter by adding zircon? If not I would try a small test using the same amount of zircon as you put in your engobe. Also, any chance you have a deflocculant? Sodium silicate by any chance? Would this be available to you in Mauritania? If you add a deflocculant then less water goes into the slip to create the same brushing consistency therefore you can create a more "concentrated" slip so to speak. I'm not seeing the blowouts with this slip, my hunch is it isn't as vitrified or at least not as tight when the body is outgassing.
Have you tried a slower bisque schedule to allow more impurities to burn out?
5 hours ago, njabeid said:but why does this happen with oxides in the glaze and not with plain clear?
Are these from the same batch of cobalt and copper carbonates as you use in England? I not what would happen if I mailed you out a tiny amount of mine to try? (going back to Rae's suggestion that they might be contaminated)
5 hours ago, njabeid said:So why is the bond better when strontium is in the picture?
Recipe?
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I can't help but think that it's the body gassing out during glaze fire. Gas is able to go through the thinner and more fluid glaze and heal any blisters / pins but same gasses coming through the engobe are disrupting the engobe and it isn't able to heal over.
Peeling engobe on the test tiles is a separate issue, not a good bond between the engobe and the body.
2 hours ago, njabeid said:Cobalt and copper are fluxes, so they should increase the glaze's COE, which should result in crazing, not in crawling.
Copper and cobalt do both act as fluxes but both will actually reduce crazing.
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3 hours ago, Pres said:
I believe that only another potter can truly appreciate a "second".
best,
Pres
It's a bit of a weird feeling when a customer almost apologies for buying a second, saying something along the lines of they prefer 2nds as they have more character.
) until the pot is bone dry. I keep slab pots right side up.
Neil Estrick's video - grab some popcorn
in Business, Marketing, and Accounting
Posted
Neil has a second video with Clayfliks, "How to Throw a Large Vase". It's another really good one, preview below.
How to Throw a Large Vase with Neil Estrick