Min

That is the exactly what lab testing does. If you follow the link I posted above for BSC you can see how they request a glaze fired sample pot, this is what they test, the fired glaze. They test for whichever oxides you pay for. Example would be if you add some stain that contains vanadium you request they test the leachate for vanadium release. It is the vanadium oxide they give you results for. Since in North America only lead and cadmium need to be below certain government approved levels on dish ware the other oxides are usually compared to drinking water levels. Many potters, most likely the overwhelming majority of us, either use a liner without any colouring oxides to be of concern or use one with very low levels of a colouring oxide. I have had a few glazes lab tested at BSC.

As Kelly said, options for having absolutely nothing to worry about in a well balanced stable glaze would be either zero colourants or just zircopax or iron. If you want to use a stain or a colouring oxide and want to ensure it’s safe then lab testing isn’t going to break the bank. It’s about $35 per oxide to get tested and piece of mind. BSC testing link https://bsclab.com/pottery-testing Home testing, using an acid such as household vinegar or lemon/lime and dishwasher testing don’t rule a glaze “in” as being suitable for food surfaces but it will rule glazes out.

Liner glaze in the pitchers?

Looks like the base glaze was applied with a hake brush.

To direct message someone click on their name or avatar (on the left side of their post). This will take you to their page. There is an icon of a small envelope near the top, click on that and follow the prompts. If you have problems myself or any of the other mod’s are happy to help.

Hi and welcome to the Forum! How wet or dry is your clay? If it's on the dry side it could just be the water of plasticity (WOPL) is too low. Can you take a coil of clay about the thickness of your finger and wrap it around your finger without it cracking? A photo of the cracking might help.

Mason puts out a Reference Chart that lists all the ingredients in each of their stains. https://www.masoncolor.com/reference-guide

I'll post this in the pinned Custer thread also.

Nope. A third firing to ^03 can definitely change the look of glazes fired to mid or high fire. In effect what you would be doing is a strike firing which can alter glazes high in colouring oxides, particularly with iron or copper.

Hi and welcome to the Forum! If you don't like the results you have so far then there isn't really anything to loose by trying the wash. As to whether it covers the glaze, probably not but something might happen, what happens is going to be trial and error. Washes can be applied then wiped or sponged off green or bisque or they can be brushed on either on top or under a glaze. I would suggest warming the piece(s) up before trying to apply the wash. If you use a copper oxide wash overtop of a glaze it would be best not to do this on a surface that could come in contact with food. Re your muddy underglaze colour with clear glaze, this can happen depending on the chemical composition of both the underglaze and the glaze insofar as the reactions between ingredients. For example green underglazes that use chrome (in the stains within the underglaze) will turn the green to a not so attractive brownish colour if the glaze contains zinc, chrome tin stains (for some pinks, reds and purples) will get bleached out if the glaze doesn't have really high calcium levels causing grayish tones to the underglaze. Colours can also be affected if the glaze is applied too thickly, underglaze can look milky and clouded.

If you do an absorption test on your clay it will tell you this. It's a good idea to test a claybody for absorption using your kiln and firing methods rather than what a clay manufacturer publishes it as. For functional ware below 1 - 1.5% is usually good. Link here on testing absorption if you need it. If the clay isn't porous for all intents and purposes and you run your pots through the dishwasher I wouldn't worry about the odd pinhole. Aesthetics are a different point, a pinhole on a pristine porcelain piece is going to stand out far more than one on a rustic piece. Ryan Coppage article here discussing bacteria growth on crazed glazes. Conclusion is if your clay is vitrified and the pots run through a dishwasher bacteria is not an issue. (article is behind a paywall but you can access 3 free articles a month) I haven't come across any literature proving pinholes harbour more bacteria than craze lines.

Glaze crawling is usually from one or two main causes. Either the glaze was too thick or the bisque was contaminated with dust or oil (from skin or hand lotion etc). Crawling can also happen when the recipe contains too high an amount of a material with excessive shrinkage but it doesn't sound like thats it in this case.

We do our own kiln repair but there is something that came to our attention regarding installing kilns. When we were shopping around for a new home insurance policy quite a number of years ago most home insurance providers wouldn't insure me unless I could prove a licensed electrician did the direct wiring for the kilns. I don't think the "Potter" designation means you have to do absolutely everything. Are we ruling out people who use pre-made dry glazes, bottled glazes, bought clay, etc. Slippery slope.

Yup. A gold and luster eraser. https://tuckers-pottery-supplies-inc.shoplightspeed.com/gold-luster-eraser.html

Thanks for answering a couple points, makes it easier to give suggestions when we have more info. I would glaze fire the tiles on waster strips of clay. These don't need to be bisque fired if they are bone dry. For waster strips I would roll out a slab of clay (same clay as the body) to about 1/8" thick and about 19" X 16" then cut it into strips about 2" wide. There can be gaps between strips but have the edge ones fairly close the edge of the tiles. Make the strips a bit thicker if you plan on glazing the edges of the tiles right the way down with no wax line. Extruded coils would work too. Reason for the waster strips (or coils) is twofold, one to allow the tiles to shrink / move freely without getting hung up on the shelves and secondly to allow airflow under the tiles. During cooling the shelf is going to retain heat much more so than the air will, this means the bottom of the large tile can be much hotter than the top surface which can lead to cracking. I would place the tiles in the middle section of the kiln. If you use half shelves make sure they are lined up perfectly. I would also suggest ringing the tiles with either other pots or square or triangular kiln posts laying on the side, this also helps even out the heating and cooling. I know you said the tiles are time sensitive so you might not have time to dry waster strips / coils, if so some people have success with using silica sand under large slabs, sculptures also. To be super safe you could also add a slow cool through the quartz inversion zone. (slow from 1100F - 1000F, tc's measure air temp not shelf temp so the 100 degree range is pretty safe) Don't open the kiln until it has cooled down well below 400F. I would also glaze fire them slowly, not a fast firing.

@Lauren F, what cone are you firing the tiles to, cone 6? How are you firing the tiles? How big is the kiln, room to put a shelf above and below the one(s) that will have the tiles? Can you slow cool the kiln?

If the colour is the same in both (I'm guessing it is if you haven't noticed a difference) then put a drop of water on a piece that was for sure bisqued to 1860F and time how long it takes to soak into the clay. Repeat with the clay that was possibly only bisqued to 1200F and see if takes longer. You can also stick your tongue on both pieces, the lower fired one will stick more. (maybe don't do this in public)

Take your claybody that the pots are made with and run it through a 60 mesh screen to remove most of the grog / sand. Brush that onto the feet of the groggy clay pots. After glaze firing rub the foot over with a diamond sanding pad.

I don't think it is. Whatever works.

Xiem BatMate is used for different purposes than the neoprene disc. My neoprene disc is about 3 mm thick. I use a Xiem BatMate (or a knockoff of it) to hold batts to the wheelhead without using batt pins but not to trim on. I know a lot of people use the Xiem BatMate to stop wobble in uneven batts with the use of pins but it works super well with plaster batts of any size and wood batts up to about 10" without pins at all. I use the neoprene only for trimming. Still have to keep a slight pressure on the top of smaller pots like mugs, no need for clay wodges to hold the pot down.

Rutile is one of those materials that can make or break a glaze, it can vary a lot from batch to batch. I would try it out with a small test batch before using it in a large bucket of glaze. Colour difference might just be your new batch hasn't been calcined.

@Morgan, have you tried slaking some of your dry scrap and seeing if it actually needs additional plasticizer? If you have been diligent in saving your slops you might not need anything. Re which one to use if you do need one, Bentone MA is what used to be called Macaloid. I have used that and also Veegum (it's not a gum either, it is a water washed white smectite clay, extremely fine particle size also). If you do need to add some plasticizer I would weigh out a KG of dry scrap and then try just 0.50 - 0.75% of either Bentone MA (Macaloid) or Veegum. If you try the Veegum be careful which Veegum you get as there other forms of Veegum available, you want either Veegum or Veegum T. Whichever you use it has to be thoroughly mixed with hot water before adding to your slaked clay. I add the Bentone MA (or Veegum) to the water then whiz it with a handheld stick blender for about 20 minutes. It will go thick and very smooth, might need to add more water if it gels up too much. Once you have the dry clay slaked down add the Bentone MA or Veegum mixture to the clay slurry and continue mixing it until it's all blended. When trying out grolleg bodies I used 3% Veegum, it made a very plastic claybody that was quite sticky, I probably could have cut that amount back. Hansen has the analysis for Bentone MA (aka Macaloid) containing MgO (approx 23%). Article on it here and on Veegum from Vanderbuilt minerals here. Either one will get the job done.

Lot of good information here @neilestrick, good of you to address all the points in such detail!

This thread is bounced off this one that was discussing extruders then went off on a bit of a tangent. I brought up the subject of thrown handles as another alternative for @Pyewackette . (other options such as cast, press molded etc in the linked thread also) Super quick demo photos below, hope this helps Pye. Throw a donut on a batt, for mug handles that need to be straight use as big a batt as you have or throw on the wheelhead if it's wider than your batts. Center the clay then open it up right down to the batt. While throwing the donut press down firmly on the clay as you are pulling it outwards from center. Clean up the edges of the donut and shape into a dome top, flat, ridged, whatever profile you need. Can use rib made from an old credit/gift card to make identical profiles for the donuts if making a lot of one style that need to be the same. Cut into the donut with a pintool then slowly rotate the wheel to cut the donut off. At this point you can either let the donut set up a bit or work it now. Cut off a section and either hold it up and smooth the cut edge or let the sections dry a little then lay them facedown and smooth the cut edge. For mug handles pull them straight and let them hang until they are dry enough to attach.