Crawling On Laguna B Mix

[blueguell]

I have been using some home made glazes for over a year now and have never had issues until I recently switched clay to laguna b mix. The clay supplier I was using was bought out so I can not go back to my old clay. I'm sure something is not agreeing between the clay and the glaze, I just don't know enough about clay and glaze chemistry to resolve it. I did a little research and tried flocculating with Epsom salt solution, but that did not help. It only happens where the glaze was dipped or on really thick. The glaze also cracks away when drying. Any help would be greatly appreciated.

[glazenerd]

Not nearly enough information to establish a specific cause: but from what I can see from the pics:

 

1. glaze is extremely fluid as indicated by the pooling and streaking I can see. >neck on brown bottle 2. (application issues as well)

2. glaze not sieved or mixed efficiently: as indicated on blue/green bottle. Blue on one side ran little, on the other side ran much,

3. over-fired- glaze is extremely fluid as mentioned, but I also see evidence of boiling.

4. old clay had much more alumina in the body compared to the new b-mix.  glazes rely heavily (but not exclusively) on leeching alumina from the clay surface to help control glaze run from fluidity.

5. contaminants on the clay surface hindered the bond ( possible but unlikely.)

 

possible combination of several of the above factors.

 

Nerd

[blueguell]

Thanks for the reply. I sieved the dry glaze through an old window screen twice before mixing with water. I then ran the liquid through a screen twice. I also mix it with a drill before each application. The glaze seems to be fairly thick since I've flocculated with Epsom salt. My guess is it may be over firing due to what you stated. I recently upgraded my kiln to one with a digital controller and I have not fired it with witness cones yet so I am not sure if the control is actually reading accurately. I will try firing with cones to see if that's the problem. Thanks again

[Min]

"I sieved the dry glaze through an old window screen twice before mixing with water."

Don't need to do this, just making more dust. Are you using the window screen for sieving the glaze after mixing with water or a finer mesh one?

 

Also, instead of going on how thick the glaze looks is a little tricky until you have used the glaze for a while. Like you said adding epsom salts makes it look thicker than it would without it. I would measure the specific gravity of the glaze instead of going by the look of it until you are getting okay results with the b-mix and these glazes. If the glazes are still too runny after getting the crawling issue sorted you can add some kaolin to stiffen the glaze up a bit. Might just be it was too thick though so I wouldn't do that until the crawling issue is taken care of and you have fired with witness cones.

[blueguell]

I used the window screen to sieve the liquid mix too. I take it that's not sufficient, (still somewhat new to this). Thanks for the advice

[Mark C.]

(The glaze also cracks away when drying.)

​you have it on to thick

[glazenerd]

 

http://www.axner.com/axner-mini-sieve.aspx

They have other models available with smaller meshes.

[Mark C.]

Get a real 80 mesh screen and run it thru once when after its wet mixed.

[preeta]

Not nearly enough information to establish a specific cause: but from what I can see from the pics:

 

1. glaze is extremely fluid as indicated by the pooling and streaking I can see. >neck on brown bottle 2. (application issues as well)

2. glaze not sieved or mixed efficiently: as indicated on blue/green bottle. Blue on one side ran little, on the other side ran much,

3. over-fired- glaze is extremely fluid as mentioned, but I also see evidence of boiling.

4. old clay had much more alumina in the body compared to the new b-mix.  glazes rely heavily (but not exclusively) on leeching alumina from the clay surface to help control glaze run from fluidity.

5. contaminants on the clay surface hindered the bond ( possible but unlikely.)

 

possible combination of several of the above factors.

 

Nerd

Nerd, THANK YOU so much for taking time to write in detail. i learnt a lot from your words. 

 

so i have a question. you said 'extremely fluid' in point 1. what makes it so fluid? rather what makes the glaze melt so much in general? the composition of the glaze? flux? or over fired? or multitude of factors?

 

in general over fired may not be a bad thing if that's the effect you want right? for instance if you want it to break over textures and discover over firing makes the glaze run more and still gives you a nice colour and lets you see the texture underneath then its ok to overfire if you understand and control it as such?

 

3. 'boiling' - Does boiling lead to blisters? is boiling due to gases escaping? would that mean all carbon did not burn out during bisque firing?

 

my knowledge of glaze is very limited. only from reading. so your post was very helpful.  

[glazenerd]

 

so i have a question. you said 'extremely fluid' in point 1. what makes it so fluid?

1. high levels of flux: one reason formula limits are handy guidelines. 2. over-firing the intended cone the glaze was formulated to. Most glazes have breathing room to go slightly under, and some higher over the target cone. However, sodium for example can turn fluid rather quickly if too much flux or too much heat: or a combination of both. Glazes that use frits or lithium are even more susceptible than sodium or potassium. 3. glaze application: obviously if you over-load a glaze, the excess is going to run. Most of the layered glazes are loaded that way intentionally to produce a running/mixing colorant look.

 

I use the terminology of "boiling", but the more common term is "felting." An area where the glaze raises above an otherwise smooth surface to create a rough and protruded spot. Sometimes you see larger pinholes with excess glaze pooled around it: another symptom of boiling, but can be caused by other factors as well. Blistering can be another symptom: rough or gritty spots under the glaze surface that have the appearance of pinholes that have not broken through the glaze surface. The difference between this and off gassing is usually in "boiling" they are grouped in clusters and the areas around them are smooth. Generally if I see pinholes in the piece and areas where there are many: I assign it to off gassing. However, if there are little to no other pinholes areas that have raised blisters that have not been broken: I look at boiling/felting.

 

The problem I have been monitoring is the marked increase in the posts about pinholes on stoneware bodies. There has been somewhat of a marked increase in problems in the last six months on the forum. In almost every case, stoneware clay is involved. I have been looking (microscope) at fire clays, and ball clays usually associated with stoneware bodies and have been seeing large (20-80 mesh) chunks of white debris in several. This could be soapstone, but it could very well be chunks of feldspar minerals. These particles laying at or near the face of the clay would certainly create some serious pinhole issues as a result of off gassing and "hot" spots of flux. I have several new 50lbs bags coming in early next week; more than curious to see if this trend continues.

 

Nerd

[neilestrick]

I would also say that there are a lot more problematic glazes on the market than there used to be. 20 years ago, when cone 6 was not as popular as it is now, the majority of the commercial glazes on the market were pretty consistent and easy to use. There have always been a few exceptions, but in general it wasn't a big problem. But now there are more brands on the market, and a lot more competition to sell glazes. Combined with peoples demand for more interesting and exotic surfaces, there are now a lot more 'iffy' glazes on the market that require very specific firing parameters for successful results, and they are runny and less stable when layered with other glazes. When they work they're beautiful, but when they don't there's a lot more pinholing, cratering, and crawling. 20 years ago they wouldn't have put those glazes into production because of the potential problems and wanting to avoid all the phone class from disgruntled potters, but the market demands it nowadays. There are some companies that are far more guilty of this than others IMHO, but in general it's much more of a problem than in the past.

[glazenerd]

Neil:

I do not use commercial glazes, but on rare occasions where it is easier to just buy a color rather than develop one. That said, I hear about the problems on a regular basis. So I would absolutely agree with your comments, and further compounded by mismatching clay to glaze. I was trying to find some info on premix glazes for a friend of mine: was rather shocked by the lack of info. I would have thought they would at least show COE values. Then on the custom mixed glazes the problems becomes glazes that have either: been written before formula limits, and/or recipes that float around on the Net that have never been properly tested. Add to that recipes pre-1999 that have custer; which is no longer viable due to dramatic changes in custer. Any time I see glaze recipes with greater than 50% of a single feldspar/potash: I am automatically suspect.

I have been talking to Ron Roy about re-releasing his book. As part of that discussion: sections on matching glazes to clays, and diagnosing glaze and clay issues: and how to resolve them. Now that I think about it: a section on testing glazes before they are put into use.

 

Nerd

 

You can see the large whitish spots in this stoneware sample:

[preeta]

Neil I am shocked by your information. That is so disheartening. it seems everyone is out to get the pottery industry. 

 

And yet ... makes sense. Some of the students who choose to buy glazes are really struggling to get the effect they see on the test tile. 

 

am enjoying the discussion here. 

[glazenerd]

Preeta:

 

In the broader sense: certain amounts of change should be expected. Many of the clay pits/ mines have been around 30-50 years: so they will dig through various levels of purity/impurities. Some clay pits are sedimentary, while  others are vast deposits left behind by glaciers moving across the terrain. As a point of interest: the southern end of a clay pit is always the finest and purest: and the northern end is the coarsest and most contaminated. The Helmer mine is only 600 acres: which in the overall scheme of things is not very much.

 

Everyone is well aware of the custer issue: but gerstley borate has gone through changes. Many potash feldspars are blended now because the consistency is just not there anymore. I have talked to several clay mines: they all note changes in product in recent years; one just changed their iron from 5.0 to 6.2: which is substantial as iron goes. I have seen some changes in alumina levels in clay as well: which if that continues will change how we formulate glaze to compensate for glaze flow due to the lack of it. There have been dramatic shifts in the industry as a whole: from the primary use of potash feldspars in the 90's to sodium feldspar today. This change is not only in glazes, but also in clays as Nep Sy is now the flux of choice for clay because of consistency, but more so price points.

 

Cone 10 is slowly fading away in electric kilns, and cone 6 is becoming the norm. I told Howard Arnold in an email recently that in the next 10 years I fully expect to see a shift to cone 1-3 firings due to electricity costs. I also expect to see a narrowing of the clay market from a multitude of products to a more select palette. There are other factors that have helped such as vastly improved milling techniques. Modern potters have the benefit of 325 mesh products; that was not always the case. As Ron Roy recently pointed out in the latest sieve testing: that a bag of 325 mesh silica only had 10% of that grade: the rest was much finer. They use magnet milling to remove heavy iron and other metals from feldspars and clays.

 

The one caution I would give every potter is to test their products every time they get new shipments. The inconsistencies are getting to the point where that is becoming almost mandatory. Rarely a week goes by on this forum that someone does not post a thread about an old product they used that is now acting strange. My advice would be that every potter keep a stack of bisq test tiles handy so they can throw a few into the next firing to check new shipments of glaze or other ingredients. I would also make a few small tiles out of every new bag of clay they receive; just to check it for changes in consistency. It is a fat pain to absorption test every new bag, the reason I put up the Nerd vitrification test. An unglazed vitrified body will not absorb water, so putting a drop of red dye on a test bar then rinsing will tell you very quickly if there is a problem that needs further examination.

 

Nerd

[neilestrick]

Well said, Nerd, and I love that you mention cone 1-3. I've been saying the same thing to my students for the last year. There's no reason to be working as hot as we do other than tradition, which seems to be the main reason things change so slowly in ceramics. Imagine doubling element life but still getting vitrified clay bodies!

 

All markets change.

[glazenerd]

Neil:

You develop the glazes, and I will work on some clay bodies for cone 2-3. We can write a book, and sell product/s. Porcelain would be fairly easy to adapt to cone 2-3: stoneware would take a little work. Switch from Nep Sy to spodumene: that should work.

Nerd

[Fred Sweet]

Nerd-

Won't spodumene bring all sorts of fit issues due to the lithium content, or did I miss something in the prior discussion?

[bciskepottery]

Neil:

You develop the glazes, and I will work on some clay bodies for cone 2-3. We can write a book, and sell product/s. Porcelain would be fairly easy to adapt to cone 2-3: stoneware would take a little work. Switch from Nep Sy to spodumene: that should work.

Nerd

Try John W. Conrad's "Cone Three Ceramic Formulas: Clay, Engobe, Stain, and Glaze", Falcon Publishing 2006

ISBN 935921-24-1

 

https://www.amazon.com/Cone-three-ceramic-formulas-engobe/dp/B007HFYPYS

[glazenerd]

 

Won't spodumene bring all sorts of fit issues due to the lithium content, or did I miss something in the prior discussion?

Fred:

Any flux that is used in glaze can be used in clay: but that does not mean they are good choices. Spodumene is a primary component is flame-ware bodies because of its expansion properties. That would create the biggest issue: dropping from a stoneware COE of 5.75 (average) to around 5.00. I would assume the primary concern would be the effect on colorants? I ran several porcelain bodies with spodumene/lithium: in conjunction with crystalline glaze. The only real problem is getting the lithium level to a workable level of molarity.  Potassium would probably be the better choice, but it also falls on the border.

 

Nerd

 

Any books on cone 4?... has to be a blank somewhere that needs filled.

[Fred Sweet]

Nerd-

I had thoughts about using lithium in both the body and glaze so as to somewhat nullify the expansion/contraction issues. Also thought about the the colorant issues, but decided I'd start one question at a time.

[neilestrick]

Neil:

You develop the glazes, and I will work on some clay bodies for cone 2-3. We can write a book, and sell product/s. Porcelain would be fairly easy to adapt to cone 2-3: stoneware would take a little work. Switch from Nep Sy to spodumene: that should work.

Nerd

 

Deal. Have you played with Pastic Vitrox in clay bodies yet? I bought some a couple of months ago specifically for trying in a cone 2 body but haven't had a chance to use it yet.

[glazenerd]

I have looked at it, a couple of concerns. The main one being very low in alumina: which would weaken the body overall. That could be overcome with other additions, then the next being KnaO levels: which could be overcome as well. I assume you are looking at it for PSD and plasticity reasons? A big factor in that cone range would be mesh size: personally I would use Imsil A-25, Minex 400, and a few other micron sized products. It would require an equal amount of flux and smaller particle sizes to compensate for less heat.

 

Nerd

[neilestrick]

I have looked at it, a couple of concerns. The main one being very low in alumina: which would weaken the body overall. That could be overcome with other additions, then the next being KnaO levels: which could be overcome as well. I assume you are looking at it for PSD and plasticity reasons? A big factor in that cone range would be mesh size: personally I would use Imsil A-25, Minex 400, and a few other micron sized products. It would require an equal amount of flux and smaller particle sizes to compensate for less heat.

 

Nerd

 

Yes, for plasticity.

[glazenerd]

 

Neil said: Have you played with Pastic Vitrox in clay bodies yet?

Made three test samples (200grams each) of stoneware:

 

Conclusion: VERY plastic...little goes a long way. 8-10% makes for a very plastic body.  Did one with 15%, ranked right up there with silly putty.

 

Nerd