Fighting bare crawling patches and they’re winning!

[Beebop]

I have been making my own glazes for about a year and half and have been fighting crawling bare patches since the beginning. Some things that have helped: power-washing bisque ware with the garden hose, glazing bisque ware slightly damp and lowering specific gravity of my glazes. Any yet, I am still getting crawling bare patches, even though they are smaller and less frequent. Also, they seem to happen a lot more on porcelain than stoneware bodies. Is there a reason why that might be? Is there a compatibility issue with my glazes and the porcelain? I’ve tried lowering Mg  in some of my recipes since I do rely pretty heavily on that to fix glaze fit issues, but it happens even with glazes that had low amount of Mg to begin with. Firing to cone 6, fast fire slow cool in an electric. Thanks!

[Bill Kielb]

If you believe William M. Carty (Alfred university) he breaks the causes up into poor wetting during application or material shrinkage.

Wetting could be things like: Dirt, oil, dust, low bisque porosity …….   Shrinkage could be during drying or sintering prior to melting.

Often this is the result of poor packing of the glaze layer. Personally most often I have run into:  the glaze cracking during drying. Simplifying further, thick glaze application can make some glazes crack during drying. Some other causes are excessive clay in the recipe and even over grinding some of the raw materials.

Post a picture or two, maybe a recipe or two and your typical application thickness if known. This will likely provide more insight for folks here.

[Beebop]

Yes cracked glazes I am learning cannot be revived no matter how much I think I can salvage them. Scrape and reglaze is key I’ve learned.  The glaze that really gets me most is Hasselberth and Roy’s clear glossy base 2 with zircopax added up to 10% on porcelain. Also my own formulation of kaki and Jun-ish glazes both with EPK under 10% with 2% added bentonite. Is it the bentonite? This  is a consistent additive in Britt’s cone 6 book so I’ve followed suit in most instances. All my photos are too large to post, so I’ll have to work on that fix first before I can share examples. Thanks!

[Bill Kielb]

One way (of many) is to email to yourself and choose to reduce them prior to sending. Most operating systems allow that.

I seem to remember reading some crawling comments with GB-2 back in the mid 80’s. I don’t think there was ever a specific cause associated with it, but I remember reading several. The glaze is fairly high in boron but stiff with 17% clay and fairly high alumina if my memory is still working. John and Ron I believe published later versions that may perform better for you.

[Beebop]

You have a good memory! Yes 17% EPK. I’ll look for variation of this glaze or try to tweak the zircopax version to reduce clay content. Thanks! 

[Min]

1 hour ago, Beebop said:

try to tweak the zircopax version to reduce clay content

Problem with this is you will be altering the qualities of the fired glaze. If a glaze with 17% EPK is crawling the easiest solution is to use calcined epk for part of the epk content. Need to allow for the LOI (loss on ignition) of the calcined epk so it's not a direct 1:1 sub. Hesselberth and Roy have 4 versions of the base glaze, one of which uses part calcined clay, link here. 

Re magnesium in glazes and shrinkage, the form the magnesium is in will make a difference to shrinkage of the glaze. The more a glaze shrinks upon drying the higher the likelihood of getting cracks in the raw glaze as it dries, cracked raw glazes are fairly certain to crawl when fired. Magnesium supplied from magnesium carbonate will has an LOI of approx 57%, super high. This is why it works so well in crawl/lichen/reticulated glazes where you actually want the glaze to crack and crawl. Magnesium supplied from dolomite has an LOI of 48%, again a high figure. Talc can vary depending on which one you have but it's likely going to be in the 6.5 - 12.5% range. Magnesium from a frit such as Ferro 3249 will have an LOI of 0%.

Considering you are having consistent problems with crawling I would be looking at the specific gravity (sg) of each of your glazes. Make up some large test tiles or use some junker bisque pots and do some systematic testing for each of your glazes. Accurately measure the sg of each glaze then time how long you dip the test piece. Dip the entire test piece once then once the sheen is off the wet glaze dip the top half with a second dip. It can be helpful to have a second set of (smaller) test tiles that you don't fire, after the glazes are dry scratch through them to see the thickness of the glaze and keep these unfired test tiles as a reference going forward. It will probably take a few test pieces for each glaze to get the sg dialled in. Once you have it then write it in your notes and on the outside of your glaze bucket plus the number of seconds you dip for.

 

 

[Beebop]

This is incredibly helpful thank you! I have been clacining EPK in my bisque firing for use in kiln wash, so I’ll look up how to sub some of the EPK in the GB2+Z recipe and also check out these modifications. I will also explore some tests on SG, I haven’t been super disciplined about that so it makes sense that this is where I need to go to get rid of bald spots. My Mg is mostly from talc, no mag carb on my shelves, so sounds like that is less likely the issue.

[Min]

7 hours ago, Beebop said:

I have been clacining EPK in my bisque firing for use in kiln wash, so I’ll look up how to sub some of the EPK in the GB2+Z recipe and also check out these modifications

This is something that would be straightforward to do with glaze calc software if you use that. If you don’t use it yet it would be a really good glaze modification to start with. If not we could give you a hand here.

[Bill Kielb]

8 hours ago, Beebop said:

so I’ll look up how to sub some of the EPK

If you are ever stuck you can just look up the loss on ignition for EPK which is 14.81% as I recall. So after calcining, for every 10 grams of regular epk you only need approximately 8.5 grams of calcined EPK. A more exacting substitution would be: non calcined EPK X 0.8519 = calcined EPK. In a pinch you could also drop your recipe into the  Glazy.org calculator, it’s free and internet based so available wherever a browser and internet connection is available. BTW: Don’t replace all your EPK with calcined, your glaze still needs some to stay suspended. Maybe leave 10% or more regular EPK.

[Beebop]

Love this very specific instruction, thank you! I’m on Glazy, I don’t know how anyone makes glazes without it!  Thanks!

[neilestrick]

If you're having crawling problems with multiple glazes, then application is probably the issue rather than the formulas. Are they crawling when used alone, or when layered? Do you have lotion on your hands when handling bisqueware?

[Beebop]

Yes multiple glazes, but GB2+Z is a big one. Layering glazes does seem to make it worse but it happen on single layer glazes as well. Lotion could totally contributing to the issue, I have not thought of that! I tend to take lotion breaks while working in general since my hands get so dry, so it’s completely possible that I am creating a resist while handling. Seems so obvious now but I will make sure I don’t keep doing that. Thanks for that. 

[Callie Beller Diesel]

3 hours ago, Beebop said:

lotion breaks

If your hands get that dry while glazing, using latex or tight fitting nitrile gloves might be your friend.

[Chilly]

8 hours ago, Beebop said:

lotion breaks while working in general

I can work with clay without gloves, but as soon as I get the glazes out, it's rubber gloves time.  Ordinary washing up ones for me.

[Pyewackette]

13 hours ago, Beebop said:

lotion breaks

I have allergies so asked for help with potter's hands awhile back here and got lots of good advice.  The thing that has worked best for me is using bag balm - REAL bag balm, not the faux trendy stuff that calls itself bag balm.  I use Dr. Naylor's in the yellow and red can, or you could go for the Vermont stuff in the green can with the red flowers or whatever those decorations are.  "Moisturizing" lotions, it turns out, generally don't moisturize all that well, hence your need to resort to more lotion multiple times throughout the day. Tractor Supply carries both brands, or you can find it at most feed stores or Amazon.

Try using some kind of balm on your hands after you're done working, after washing dishes, before you go to bed, after shower/bath.  I can't use any lotions AT ALL and just applying the bag balm once or twice a day has fixed my hands right up. It smells funny for a little while but you get used to it.

Lanolin based balms and even plain ol' vaseline can help - though with the vaseline I would suggest only using that right before bed and covering your hands with old socks or mittens so the vaseline stays mostly on your hands and not on your sheets LOL!

[neilestrick]

I had a student who was having random crawling issues and it was totally from lotion on her hands.

[Mark C.]

Never handle bisque ware with oils on hands-I have never wet pots before glazing unless they are dusty and need that washed off.

Most likely the tips you alredat got will help-Mins calcined epk and not hand lotion in studio on glaze day.

The last issue is glaze thickness if its to thick or many layers this can make for crawling

I;'m a all porcealin studio

[Beebop]

On 4/15/2022 at 7:19 AM, Pyewackette said:

 The thing that has worked best for me is using bag balm - REAL bag balm, not the faux trendy stuff that calls itself bag balm. 

i’ve never even heard of bag balm but i’m sold, the tip is much appreciated! living in the low desert on top of working with clay has done a number on my hands, no amount of lotion is ever enough!  

[Pyewackette]

@Beebop I'm in a very dry area (we currently have wildfire alerts) and I came from an even DRIER area, the High Sierra Desert.  I was at 5600 feet elevation on top of it. It used to get so dry my ears would bleed, and I would hang a wet washcloth on top of my head to alleviate the dry eye.

I've also found hemp oil to be very helpful in these sorts of dry conditions.  Not CBD.  Just hemp seed oil like you can get at the grocery store.  It smells woody-herby (like dry grass to me) but put a few drops of lemongrass oil or your favorite pure essential oil in it and it covers that odor up.  Before I figured out what I was allergic to (palm products, including everything derived from coconut) one day when I ran out of my permascription for cortisone cream - the doctor's answer to my mystery rashes - in desperation I rubbed some hemp seed oil on and it worked WAY BETTER to alleviate the itching and dryness than the cortisone cream ever had.

Hemp seed oil is very well absorbed into the skin.  Now I use both the hemp seed oil and the bag balm.  The bag balm takes care of the worst dry patches on heels and elbows like a champ, too.  I don't need that expensive foot cream with urea in it (which I'm probably allergic to anyway LOL!)

While you can alleviate the aroma of hemp seed oil, pretty much nothing will cover up the scent of lanolin.  But it doesn't hang around that long and like I said, you get used to it.  It probably also helps that my mother used to use bag balm on us in the long ago times when I was a kid so the scent isn't all that unfamiliar to me.

Hope it works as well for you.  I do know dry and it ain't fun.

BTW, as others have mentioned, don't use anything on your hands before you work with clay or pottery.  It will rub off onto the piece and mess stuff up.

Also keep in mind - whatever is on your hands will get into the clay water.  We have reclaim buckets at the studio and I got a rash on my hands because someone with lotion on their hands managed to transfer some of that into the reclaim, probably from their slops.  I don't know what that might do to the reclaim but it sure did a number on my hands.  Now I keep my own reclaim bucket and just add that to the studio reclaim.

[Harold Roberts]

Back to the topic of crawling, I single fire most of the time and have had trouble with crawling especially on overlapping glazes even if I let the glaze dry out before overlapping. I believe it is the dry dusty surface of some of my glazes. I now add dextrin to my glazes and no longer have those troubles.

[Hulk]

Interesting! Thank you

Binders for Ceramic Bodies (digitalfire.com)

[Min]

MAGMA from Brackers works a treat for this too.