Crawl & Lichen Glaze problems

[Ravi Ivaturi]

Hi, I've been trying a lot of John Britt cone 6 crawl glazes (1230 degrees C) and a few lichen glazes cone 04 1060 degrees C) (from other authors.  I've done a few test tiles but NOT able to get the effects.  Whilst making the glaze, I used 1:1 ratio ie glaze to water so if there is 100 gms of glaze, I used 100 ml of water.  I've been told to use a  1:2 ratio is 100 gms of glaze with 200 ml of water.  Is this true?  Also do I need to use a UGM (Universal General Medium) too.  Would appreciate your comments please.  

[liambesaw]

The glazes have to be thick like pudding, very gel-like, and they must crack when drying for the crawling to happen.

[Ravi Ivaturi]

Thanks for your note. I did various tests on the thickness and initially I had it very thick like you mentioned but it didn’t crack when drying. It just stayed on the tile like a normal glaze. Does it mean that there is too much general medium or less water in the glaze. When mixing a crawl glaze or lichen how much water / general medium do you generally use? 

[liambesaw]

19 minutes ago, Ravi Ivaturi said:

Thanks for your note. I did various tests on the thickness and initially I had it very thick like you mentioned but it didn’t crack when drying. It just stayed on the tile like a normal glaze. Does it mean that there is too much general medium or less water in the glaze. When mixing a crawl glaze or lichen how much water / general medium do you generally use? 

I don't remember what my water measurement was, I just mixed it up like I would a normal glaze and it gelled by the next day.  Adding water makes sense though, since it will shrink more with more water, causing the cracking.

[Ravi Ivaturi]

Liambesaw many thanks. Will give it a try in tweaking the glaze and let’s see what happens. 

[Min]

5 hours ago, Ravi Ivaturi said:

Universal General Medium

Is this a glycerin based medium? Are you planning on brushing the crawl glaze or dipping / pouring? When I was using crawl glazes I did a bit with brushing but mostly poured them. For the brushing glaze I used approx 1 part CMC brushing medium to 2 parts water when mixing the glaze up. You can make your own CMC brushing medium by sprinkling 1 1/2 tablespoons of CMC powder onto 1 gallon of hot water and 1/2 tsp copper carb. Let it sit overnight then mix it up really well. (the copper carb acts as a preservative and is little enough that it shouldn't effect the colour of the glaze)

5 hours ago, Ravi Ivaturi said:

I've been told to use a  1:2 ratio is 100 gms of glaze with 200 ml of water.  Is this true?

I wouldn't think this would be a good idea. Crawl glazes need to be thick to work, with this much water they are going to be very runny. Glaze needs to be nearly as thick as pancake batter, a small artists paintbrush should be able to stand up in it. If you don't see cracks in the raw glaze as it dries on the pot then it won't crawl in the firing. When you get the glaze to the consistency that works then measure the specific gravity of it so you can replicate it. (a search on the main page will bring up methods of measuring specific gravity if you need instructions)

Welcome to the forum!

[oldlady]

a few years ago there was a similar question about ratio of glaze to water in ordinary, not crawling recipes and the consensus was about 2/3 weight of water to glaze.   100 grams glaze, 67 grams water.

[Ravi Ivaturi]

Brilliant.  Many thanks for your kind feedback Min & Oldlady. I guess I need to redo my crawl and lichen glazes as I have a ratio of 1:2 (glaze to water) and the glaze looks very runny! Although it dried fast on the test tile, there were slight pin holes tend to brush my glaze as well rather than dip them. I plan to have two batches of the glaze, one with only water and the other with a medium and water and check the results out. 
I have uploaded a couple of images. One is a fired test tile where the extreme left and right had a bit of a crawl and the glaze had only water mixed in it. The center two had a mixture of medium and water and looked thick but took a while to dry on the test tile and did not show any sign of crack on the tile. The other photo is a glaze due to be fired. This too doesn’t have any cracks on the time. Here the glaze was runny band I dipped it twice to get some thickness but still no signs of crack although the glaze dried faster! 

[liambesaw]

None of those look nearly thick enough

[Ravi Ivaturi]

Ok thanks. Clearly I got the water to glaze mixtures wrong. My glazes are too runny. Looks like I need a thick paste like slurry that dries fast and also shows signs of cracks on the test tile even before firing. 

[Ravi Ivaturi]

Hi everyone, just to clarify on the mixing ratio for brushing for a crawl glaze..for 100 gms of glaze powder, I need to add 33.5 ml of medium and 67 ml of water and for dipping..for 100 gms, I need to add 67 ml of water. 
Is that right? 

[Min]

18 minutes ago, Ravi Ivaturi said:

Hi everyone, just to clarify on the mixing ratio for brushing for a crawl glaze..for 100 gms of glaze powder, I need to add 33.5 ml of medium and 67 ml of water and for dipping..for 100 gms, I need to add 67 ml of water. 
Is that right? 

When @oldlady mentioned that 100 grams glaze : 67 grams of water she was referring to a thread where the discussion did not include crawl glazes. That ratio is just a general starting point for dipping glazes. Many variables including glaze composition; fritted glazes are going to need less water than those heavy in clay or gerstley borate for example. How porous the bisqueware is, how long one dips for, double or single glaze layers etc.

In general a typical glaze is going to need relatively less water for a spraying or brushing glaze versus a dipping one. Crawls are not typical glazes. 

We don't know what your brushing medium is so it's hard to answer that question. For dipping or pouring  I would suggest adding 50 grams of water, mix it up and let it slake a few hours, if the  50 grams of water isn't enough then add just enough to make a thick slurry, thick like crepe or runny pancake batter, to 100 grams of dry glaze base. After it's slaked put a small amount on a test tile, after a few minutes you should see cracks forming. If it all cracks and falls off then it's too thick so add some more water and repeat. BTW crawl glazes are notorious for flaking off the pots, use a good layer of kiln wash or a waster thin slab of clay under your test tiles. 

[Ravi Ivaturi]

Min and everyone,  this is such valuable advice for a novice potter like me. Many many thanks. Will give it a go and test them.  Will post the results. 

[Ravi Ivaturi]

Hi everyone,

Here are a few test tiles on the crawl glazes based on your inputs.  I fired them to Cone 6 (1230 degrees C with a 20 min soak and natural cooling) & to cone 05 (1050 degrees C with a 20 min soak and natural cooling).  

The ones in cone 6 is white and blue bubble gum colour (I got the colour wrong!) is a thick tooth paste like sludge and had a thick crawl which I didn't like much and I trust I should dilute this a bit.  The SG is close to 185 on this.

The dark blue and green lichen crawl was like a thick batter consistency and I did like the crawl a bit.  The SG on this 175.  

I used only water and no brush on medium was used.  I however used a hake brush to brush on the glaze on the test tile rather than dipping them.  I would like the crawl to be a bit of pronounced and crack a bit more.  Should I dilute the glaze with a bit of water.  Kindly let me know your suggestions.  

[Min]

5 hours ago, Ravi Ivaturi said:

I fired them to Cone 6 (1230 degrees C with a 20 min soak and natural cooling) & to cone 05 (1050 degrees C with a 20 min soak and natural cooling).  

^6 plus a 20 minute soak is going to be more like cone 7. Try more water and see what happens. If the ^6 one is too melted marshmallow looking for you when firing to ^6 you could reduce the flux to get less melting, don't reduce the magnesium carb though.

If you are looking for another dry looking low fire crawl to try have a look at the work of Mary Fox, she makes pots with beautiful crawl glazes. She mentions using Mark's Crawl.

 

[Ravi Ivaturi]

Thanks for your feedback Min.   I do have the recipe that you posted and the bottom two test tiles are from Mark's crawl glaze recipe fired to ^04.  I'll try reducing nepheline syenite in the ^6 johns britt's glaze and add a bit more water.