Min

Could you be a little more specific in what you are asking for resource recommendations with? It's a fairly broad question so if it could be narrowed down a bit it might help get more specific replies. Bisque firing, glaze firing, firing schedules, down firing, drop and hold schedules, preprogrammed schedules versus using a custom schedule or something else? For glaze reactions are you looking for commercial glaze reactions resources, recipe resources, reactive glazes info, or something else? Type of clay you are using at cone 6, is it a dark claybody or a light firing one etc. Do you need info on why some claybodies and/or glazes are more prone to glaze faults or how to troubleshoot glazes or ? Are you making functional pots, using commercial glazes or mixing your own? Need help choosing some recipes? Does the kiln have a controller or is it manual? Congrats on getting your own kiln!

Don't know how long the current clay tech has been there, she might know what happened. CAC is under different ownership since this happened so not sure if the current owner, Quinn, would know either. All I heard was it was put down to being the water.

My go to for lithia is using spodumene, my local ceramic supply price is currently $453 for a 5 kg / 11 lb bag. Lithium carb is $863 for a 2.5 kg / 5.6 lb bag. I guess suppliers need to sell the old stock before bringing in new and hopefully less costly new supply.

I would expect there are going to be other commercial glazes, such as the fake Shino’s, that will be getting very expensive or discontinued due to the cost of lithium.

Hi and welcome to the forum! Looking at images of Amaco's Ancient Copper it appears to be a high iron red glaze. There are many many published glazes with different names for iron reds (in oxidation firing). One very popular one is Bailey Red, here is a version of it from Glazy. Lithium is still available but it has gotten ridiculously expensive. Other recipes that contain lithia might have it sourced from other sources than lithium carbonate. ( frits, spodumene, petalite, or lepidolite) Bone ash (or tricalcium phosphate) is often found in Iron Red's also. I would suggest doing a search on Glazy and Google for Iron Reds and start testing. Type of red iron oxide used and the cooling schedule can play a part in how they differ also. If your wife uses it as a brushing glaze then you would need to add a brushing medium (gum) to your glaze. You can make your own brushing medium or purchase ready made medium.

Magnesium zirconium silicate acts as an opacifier, don’t know how much the magnesium plays into the opacifacation though. https://digitalfire.com/material/magnesium+zirconium+silicate

I would suggest that we do if fact know this is what is happening. We don't use oxides in isolation with just SIO2. From the Hamer and Hamer in the "Eutectic Mixture" entry starting with the paragraph that begins "Eutectic mixtures in glazes are not a simple matter of one oxide with silica but a case of each oxide reacting with every other...." then the continues for a few paragraphs down to "...would be a transparent, if coloured, glass." In a nutshell what they are saying in Hamer and Hamer is the oxides don't work in isolation, one oxide will form a eutectic with another then once that is complete the other oxides will get involved in the melt. Adding heat excites the molecules as does adding more than one other type of oxide / molecule. Bloomfield also confirmed that CaO + MgO with SiO2 will create a eutectic that melts well below that of MgO + SiO2 alone. Yes. Excess MgO isn't going to be taken into the melt, just as excess Al2O3 (or many other oxides) won't be and will result in a matte or opacified type glaze. But the fact that we can readily get a transparent glaze that contains MgO does indicate it is taken into the melt and is acting as a flux within certain boundaries. (@Hulk, dinner was a success, house was a disaster zone afterwards though!)

Is this a commercial brushing glaze, a commercial dipping glaze or a recipe you mixed yourself? How are you determining how thick to apply it? Is this a cone 4 glaze specifically, does your clay mature at cone 4? F it’s mixed from a recipe post it here. Glaze crawling like you are experiencing has a few main reasons why it occurs. Contamination of pot surface by dust or lotion/oils on hands, glaze application too thick or raw glaze has excessive shrinkage. Reason it’s that yellowish colour where it has crawled into little islands is because it’s thicker there from the glaze crawling together.

I've used a lot of Spectrum underglazes (plus some Speedball, Crysanthos and SPs ones). I've had some lumpy ones that I've needed to sieve but never they have never been grainy. The black on the bowl is Spectrum (blue is too). 3 coats of thinned down u.g. with water. Spectrum can be even thicker than Speedball, I add water to make a consistency that can drip off the the tip of the brush, wipe it against the edge of the container then brush it on. I would try thinning a test amount of yours down even more than you have been with just water and do some test tiles with it. See how many coats of diluted u.g. get you the coverage you need.

@Jodie Parry, every once in a while we get posts like yours that are asking members of the forum questions for their research or product development. I've yet to see one where the OP comes back and shares the results of their questions. This might be why you are getting few responses, in addition to the request from Marilyn for some clarification of what "digital element" would mean.

I would have a look at Johanna DeMaine’s work, she does absolutely gorgeous work with lustres. Link below to a short article by her, she also has a page on the book of faces if you use that. I would reach out to her. https://demaine.org/wp-content/uploads/2022/04/lustre-ceramics-monthly.pdf Welcome to the forum!

Why the Darvan and not just water? Darvan is going to slow down the drying time. I have found that each coat needs to be dry before putting on the next.

Hi and welcome to the forum! What type of wire are you using? How heavy are the ornaments? Could you post a picture of the setup?

Yes! #1 Pottery Plaster should be used within 6 months of the manufacturer date stamped on the full bags.

I made a comment in the thread leading up to this one in regards to Linda Bloomfield and her statement that magnesium starts fluxing at 2138F/1170C. This temperature was pulled from her Feb 2016 Ceramics Monthly article titled Phase and Eutectics. I contacted her and asked where she got her data from for that number. She very kindly emailed me back and said it was from Hamer and Hamer The Potter's Dictionary of Materials and Techniques. I can't do a screen shot of the pages for copyright reasons but if you have a copy the "Eutectic mixture" and "Magnesia" entries cover it thoroughly and is where Bloomfield got her 2138F figure from. In a very condensed nutshell Hamer and Hamer say given calcium is in just about every glaze with magnesium, (though the magnesia-alumina-silica eutectic is at a higher temp than calcia-alumina-silica), in practice, the glaze usually starts to melt closer to the calcia-alumina-silica eutectic at 1170°C. Potassium and sodium will also be present in most glazes, so these will bring the melting temperature down even further. The degree to which magnesia acts as a flux varies. Below 1170C it acts as a refractory, from 1190C through 1230C fluxing is "most marked". When used as an auxiliary or secondary flux, at under 0.25 molar it can greatly increase glaze fluidity. @BobMagnuson, if you don't have a copy of that text send me a pm and we can figure out a way for me to get those sections to you. If you still would like for me to run those tests I'm happy to do so but I really don't think it necessary given the info from Hamer and Hamer. It also meshes with my experience using a fair bit of magnesium in my low expansion glazes. (plus I have 16 people coming for dinner this weekend)

Sure, let me know how much silica you want me to add. Just to confirm it's this one? https://glazy.org/recipes/19734 I did try that a few years (as published) ago and it was really unsuccessful for me, cutlery marked really badly and stained from the sumi ink.

@grackle, for dark clays or those with a lot of impurities to burn out it's important to slow the bisque firing down between 1300F through to 1650F. It's in this temperature range inorganic carbons will burn out. Try slowing your bisque firing down 60 -100 degrees F per hour and see if that helps. For dark clays coloured with manganese try firing to only cone 5. Another way to get a nice matte glaze and be able to adjust how matte you want it is to blend a gloss glaze (without colourants or opacifiers) with a quite matte glaze. If you do a simple line blend with the gloss and add increments of 10% of a matte glaze you can see how adding the matte will negate some of the gloss. If you want to try this a good recipe to use is this one. Once you have the level of mattness (if that's a word) you like then add zircopax (approx 10%) or tin (approx 5%). If you find the zircopax makes it too matte (because it adds silica also) then tweak the gloss slightly higher.

Yup, I'm familiar with boron levels but for the purposes of this experiment boron levels are not the issue. I would rather just change one variable at a time. Not looking at the hardness, durability etc of this glaze, just the effect the magnesium has on it. If you have a recipe for a clear gloss that contains magnesium sourced from talc I'm more than happy to add that to the testing I'll do this week.

You can get a similar look by squeezing a natural sponge in thick slip then firing that. I tried it with different sponges and the rougher sponges with the larger holes did turned out well. I found inexpensive sponges that were a bit rough looking at a dollar store. What worked for me was to get the sponge wet with water first then squeeze the water out really well then squeeze the sponge in a container of slip. I was using porcelain slip made from a pugged clay, nothing but water added to it. Link here which showing another members work with it. https://community.ceramicartsdaily.org/topic/17192-clay-sponge-slip-submerged-sponge/

I thought about that but my logic was if the magnesium isn't working as a flux then it won't come into play as such in either recipe so wanted to keep the other variables at a constant if that is indeed the correct scenario.

This thread is jumping off from this one where the subject of the efficacy of magnesium as a flux in a cone 6 glaze came up and the prospect that the magnesium alumino-silicate eutectic is unlikely to form at cone 6. It's probably best to read that thread for background before this one. To test whether or not magnesium acts as a flux at cone 6 I'm going to run a test with the glaze below. Purpose of the test is to see what effect the MgO has on the melt. I know the first version of it does melt well at cone 6 and results in a clear gloss glaze. For the second version I have removed the talc (that supplied nearly all the magnesium). I have rebalanced the silica and alumina but left everything else the same. Testing if the removal of the talc effects the melt fluidity of the glaze. In theory the first glaze should have more fluidity if the MgO is acting as a flux. There is 0.1 MgO left but this is as low as I can get it without messing around with the other materials. It's a bit of a wonky recipe insofar as materials used and totals as it was part of an experiment I was doing blending different recipes. @BobMagnuson, does this look like a suitable recipe candidate for this test? Also, if anyone has the eutectics for a boron calcium magnesium silica alumina melt that would be terrific! Or even one with boron magnesium alumina silica. I found some for boron + magnesium here. The last column is in degrees C.

Have a look at this article, it goes into how MgO works at mid range acting as a flux at around ^6 compared to lowfire where it acts more as a refractory agent causing the glaze to opacify. Yes, there is a limit to how much of it will be taken into the melt. I'll start a new thread on how MgO effects glaze melt.

Adding one more suggestion, take some of your claybody and make it into a very thick slip.Add a drop or two of Darvan to about a cup of the slip then brush it through a 60 mesh sieve. Once the pots are leatherhard brush or dip a thin coating of slip over the rims and base/foot. I would do this after burnishing the grog back into the clay. Since the slip is the same as the body there won’t be glaze fit or colour issues. The grog free slip will give you a much smoother finish.

Super interesting for sure! My clear has .25 magnesium (from frit) in the unity formula. I’ll try and remove it to get rid of the magnesium and use a magnesium free frit(s) to keep frit percentage the same (given Frits in general melt easier than most raw materials) and see what happens. If you have a suggestion for any glaze test comparisons let me know and I’ll run those too. I’m firing (^6) next week. another edit: I'm going with a MgO matte (with slow cooling) that used talc to supply MgO instead. I have stumbled across an article from NASA where they used calcium, magnesium (plus silica & alumina) to make a glass, I seem to recall the melting point wasn’t exceptionally high, I’ll try and find the article tomorrow. I think there was a phase diagram in the article. edit: @Marie Lu, we have gone off topic a bit here. Debating over the effect of magnesium in regards to fluxing at^6, I do think it acts as an auxiliary flux but open to discussion and experimentation.

I don't use Stroke & Coat so I went ahead and emailed Mayco, their response below. How well the underglaze will show through is something you will have to test.