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Min

Member Since 31 Mar 2010
Offline Last Active Sep 26 2016 11:37 AM
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#113807 Multiple Clay Explosions In Bisque

Posted by Min on 26 September 2016 - 11:19 AM

pssst, air bubbles don't blow up pots. Damp pots do. Set your kiln sitter for 12 hours,  turn on the bottom element to the lowest setting and leave the peeps out. If you are making regular thickness pots then try this candling overnight or at least for a few hours. (don't forget to turn the dial on the sitter back up again before you bisque fire so it doesn't time out)

 

edit: I just re-read your second post, I missed this bit the first time:  "For a smaller kiln I think an hour per each switch is plenty of enough time to warm up and let any extra moisture escape" doesn't matter what size the kiln is the clay still has to go through the same processes, think you are firing too fast also. 




#113632 Low Fire White Clay Body Recipe For Commercial Glazes

Posted by Min on 23 September 2016 - 02:27 AM

I think this is getting way more complicated than it needs to be.

 

Totally Ceramics does slip casting with low fire white clay, they are local, they have years of experience, I would just go in and talk to them.

 

Greenbarn can order in anything from Plainsman, they are one of their distributors. 

 

Seattle Pottery Supply is a much larger store than Tacoma Clay Arts Center but I'm guessing they both carry only a few casting slips. Both good places, SPS is usually a bit less expensive than Tacoma but I find Tacoma staff are more helpful. Nope, I haven't used that Laguna slip.

 

A vitrified body, like what Joel posted, is not necessary for the sculptural work you are doing, will cost a lot more to make and bring far more variables into play. I'm sure it has possibilities as would Nerd's recipe but do you really need to start experimenting with it when you are new to all this?




#113550 The Only Absolutely True Rule For Potters. Pay Attention To This

Posted by Min on 21 September 2016 - 08:02 PM

Another absolute truth, if you have a custom order for a pot and just make 1 of it, it will screw up, if you make 2 they will both be perfect. I know this and yet I still go for it (1 oversized butter dish custom order right now, yup just made the 1 :wacko: )




#113467 Causes For Cracks

Posted by Min on 20 September 2016 - 10:38 AM

Another way slightly different to get even bottom thickness is to make one of these depth measuring pin tools. Tap a sewing needle or pin into the bottom of a hardwood dowel, chopstick, paintbrush handle, whatever, then snip it off with side cutters to the depth you want the base. For wide items you use it in a few spots across the base. (this one is for a no trim base on wide pots, the needle is fine so it's kinda hard to see)

 

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#113211 Low Fire Shino - Is It Food Safe?

Posted by Min on 15 September 2016 - 10:33 AM

@ qwrkygrrl, I use Insight level 2 glaze calc program. Yup, ^6 will give you less headaches for functional pots.




#113159 Low Fire Shino - Is It Food Safe?

Posted by Min on 14 September 2016 - 07:41 PM

Don’t know how much glaze chem you know so apologies in advance if any of this sounds condescending.

In basic terms, a glaze (for food bearing surfaces) needs to have a certain minimum amount of both silica and alumina in it. Alumina and silica make the glaze more durable and able keep stuff from leaching out of it. The flux(es) also need to be within reasonable amounts.

What this means is anything like cobalt, manganese, copper, etc, whether from an oxide, carbonate or stain is not going to stay locked up in the glaze matrix if the silica and alumina levels fall short. The glaze shouldn't loose gloss or show other signs of deterioration over time. The further away from the minimum target level the more unstable it’s going to be.

In the image below, your recipe has been converted to a unity formula. Your glaze make up the figures in the purple box. The other box shows “targets” for a ^04 - ^02 traditional lead-free glaze. Have a look at the alumina (Al2O3) and silica (SiO2) row. I think you can answer your own question about whether this glaze going to be suitable for food.

As far as lithium levels go you are going to have to do your own testing here. I don't like seeing more than about 5 or 6% lithium carb, but I've seen glazes use more than that. You are getting into an area of thermal expansion here. Glazes that are very high in lithia are by nature going to have a lower coefficient of expansion, have to test on your claybody to see if it fits. Lithia can cause both crazing and shivering on the same pot if the level is too high. Shivering glazes are dangerous, you can have a sliver of glaze (glass) come off the pot (usually on rims and high points) and get into the food/bevies. This is how I test a glaze for shivering; make a thin walled cylinder and glaze the inside only with a thick layer of glaze, include the rim but not the outside of the pot. Fire the cylinder then put it in the coldest part of a deep freezer overnight. Frozen cylinder goes in the sink then gets filled with boiling water then the cycle is repeated a couple times. Hopefully nothing shivers off. (don't know if that's the best way to test for it but it's what I do, same test to check for dunting with low expansion glazes - pot will split in two if really bad fit)


Hope some of this made sense.

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#113121 Sponge Holder Pricing

Posted by Min on 14 September 2016 - 10:41 AM

To get around the ick feel a lot of customers have with using sponges I put one of those rectangular pot scrubbies in one instead of a sponge. Even if it has a sponge inside the scrubby material it seems more sanitary and I get less comments about sponges and harbouring bacteria.

 

one of these thingies

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#113009 Throwers Sign Language?

Posted by Min on 13 September 2016 - 10:50 AM

I stumbled across these images of hand positions while throwing, from tortus - copenhagen. Thought they were beautifully done. You can see the clay even though its not there.

 

 

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#112790 Adding A 2Nd Medium To Booth

Posted by Min on 08 September 2016 - 02:49 PM

 It would also help if there are a number of items that incorporate both wood and clay.

 

+1 for everything that has already been said re 2 mediums. IMHO what Neil said above is the best way I could think of to do this if you really have to though. One of my girls keeps bugging me to make beer sampler trays, wood base plus clay cups. This kinda thing but in clay / wood.

 

photo+(117).JPG




#112527 Anti-Fatique Matts

Posted by Min on 03 September 2016 - 10:06 PM

Clearly the bearded one expects the anti-fatigue rays to be zapped out toward him from all directions, and is clearly doing something wrong. What could that be? Well, my hunch is the fatal flaw is that they are all hung upside down. Clearly...I am quite sure about this.

 

either that or the bearded one thinks we should be working in rooms with padded walls? 




#112526 Pitting Issue!

Posted by Min on 03 September 2016 - 09:55 PM

Min, your response is interesting to me. I'm just now working on learning the intricacies of glaze firing, and have had issues with pitting in my first two loads.

How long to you soak (I am firing to ^6 with Amaco glazes, on ^6 white clay) on your first and second soaking? I do now have a new kiln with an electronic controller (was simply a kiln sitter, a pyrometer, an old kiln, and me having quality time together) to help me out. Right now I feel like I did while learning to make fudge - it's all alchemy...sometimes the magic happens and you get something luscious; sometimes you have something to be desired....

 

Tarantara, I'm happy to give you my firing schedule with the double soak. It works with my kiln(s) and glazes but you would have to try it and probably tweak it to work with your kiln / glazes. If you do give my schedule a go please use witness cones to adjust soak times to bring your cone down to how it works for you. (temps in Fahrenheit)

 

250 hr to 250 no soak  (I sometimes fire pots when glazes still damp so this slow rise dries them out)

350 hr to 1900 no soak (sometimes I increase this to 400 hr)

108 hr to 2180 soak for 15 (cone 6 tip just barely touching shelf)

9999 hr to 2100 soak for 15

200 hr to 1400 no soak (i use this step so my smaller kiln cools similarly to my big kiln so my semi matte glazes look the same)

 

(psst, a really good fudge recipe is the Crazy Maime one, it never fails or turns into chocolate soup)




#112488 Pitting Issue!

Posted by Min on 03 September 2016 - 11:06 AM

Re using a ^6 - 10 range clay for functional pots. 

 

That is too broad a range of maturing temps for functional pots. It’s either going to be immature at the low end and / or over fired at the top end. Simple test, make a cylinder with a flat base and put it in the next glaze firing with no glaze on it. Then take the fired pot and fill it with water and place it on a sheet of newsprint. Leave it alone for a few days. Check the newsprint for any wrinkling. I’m guessing it will be wrinkled which would mean your functional pots will leak over time. Also, the unglazed base will soak up water from washing, which will cause eventual crazing of the glazes and also cause problems when used in a microwave.

 

Re pinholes and pitting in fired glazes. 

 

Pinholes and pitting are usually caused by a couple things, firstly, something in the clay that is burning out and off gassing through the glaze. Secondly, something in the glaze itself that is off gassing. The glaze hasn't been given enough time to heal over, different materials off gas at different temps but can usually be smoothed over at the top temp. (Can also be because the glaze is too stiff but I don’t think its this since you are getting mixed results of okay and pinholes. You can also get pitting over heavily grogged clay, especially where it is trimmed but I don’t think thats the culprit either with the description you gave of your clay.)

 

I would ask the tech who fires the kiln for the firing schedules, the cone they bisque to plus if the kilns are well vented, downdraft vent? If they are leaving the kilns to fire unattended overnight then I’m guessing they have an electronic controller so it should be possible to add a soak at the end of a glaze fire to give time for the pinholes / pits to heal over. I’ve added a second soak to my firing schedule on the way down, it has helped reduce pinholes in one of my problem glazes.




#112321 Very Cool Ulexite Oil Spot Glaze, Cone 6

Posted by Min on 31 August 2016 - 11:33 AM

Hi Jed,

You can order a sample from Plainsman Clay in Canada. Tony has a few glazes where he has experimented with it.

link on this page: https://digitalfire....exite_1657.html




#111427 Making A Glaze More Runny

Posted by Min on 15 August 2016 - 07:50 PM

This topic came up a few months ago and Paul Lewing seemed to have the best answer,

"Posted 25 March 2016 - 08:41 AM

The solutions to your problem that have been proposed have all been process or physical fixes, but the root of your problem is chemical.  If you want glazes to bleed a long way into each other, they need to be very dissimilar.  Conversely, glazes that are similar will bleed into each other less.  And the key area of difference is Si:Al ratio.  If the two have ratios have difference from each other that is greater than 6 they will definitely bleed a lot.  For instance if one has a Si:/Al ratio of 5 and the other has a ratio of 12, expect a lot of bleeding.  This of course makes sense.  One is deficient in silica, the other is deficient in alumina, so the go looking for what they need in the other.

So... bottom line, if you want no bleeding at all, your best bet is color variations on the same glaze.  Doesn't matter what glaze it is.  The the only variable will be how much of a flux or refractory the colorant is in each different color variation."

 

An easy way to make your G1216M glaze more runny would be to just decrease the alumina, (epk in this recipe), test by running a line blend. It will increase the likelihood of crazing though.




#111340 Supplies To Buy When Buying A First Wheel?

Posted by Min on 13 August 2016 - 02:31 PM

I think even your 24 gauge aluminum is going to be thick for a flexible metal rib. I put a micrometer on one of my stainless ones and it’s 0 point 1 mm.  Your aluminum might be good for rigid ribs though.

 

I personally don’t like the Xiem soft rib that I have, it’s way too thick compared to the Sherrill (MudTools) ones, doesn’t bend as nicely so kinda defeats the purpose of buying a soft one. 

 

For foam, you can save yourself some money and just use some scraps of upholstery foam when throwing, the high density stuff lasts ages. (Robin Hopper workshop tip) Old chair cushion or scraps from a foam shop. A cleaning cloth for eye glasses works really well for smoothing rims and never seem to wear out.

 

Pic of the thickness difference between soft Xiem (orange) and Sherrill (red) soft ribs. Plus a flexible stainless one.

 

 (you can kind of see the difference in the rib thicknesses)

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