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Low-fire glazes, asking for advice

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I'm asking for advice, opinions & experiences about low-fire-glazes. I'm a beginner and still unsatisfied with my glazing. I don't get rid of the little pits, pins & blisters ... sometimes only a few, sometimes only visible by looking from the side to the light ... tiny pits, the surface is not completely smooth. More on the horizontal surface.

I also have difficulties with an even brush-on ... but I have realized that some glazes are easier than others for a beginner to brush-on. I had the opportunity to use the glaze "Spectrum Metallic" and this is very nice to brush-on ... but maybe this is different with another series of this brand ...?

My wishlist:
Low-fire Glaze for the white earthenware clay
ready to use brush-on commercial glaze
bright, vibrant, intensive, rich color
glossy, shiny
food safe
not too runny (able to brush details ... for example dots should stay as dots)
easy, smooth to brush on

Before I buy a batch of glazes I'm asking kindly for your advice.

In one of the topics Gregory Hendren a Member mentioned that he bought low-fire glazes from Duncan, Amaco & Spectrum. Would be great if he could tell about his experiences with these glazes. I also read there is another glaze named Speedball. Has anyone experience with this glaze ... or with another?

I'm thankful for all advice & suggestions which could bring me out of my beginner-depression.
 

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Maybe just get a few small jars to try and see what works for you...

I mix most of my glazes, but do use some commercial glazes, among them Duncan, Mayco and Speedball. I have used Amaco glazes too.

Speedball glazes are the best ones for brushing, but the color options are very limited and many of them are rather ugly when used on red clay or just plain ugly in any type of clay. I have tried to find which gum/adhesive/suspender they use (smell like a gluestick I used in grade school of which I can’t remember the name ) but no luck so far… They aren’t vibrant in color, probably not what you are looking for. I like the white, black, blue and Purple glazes.

Other than that is not easy to generalize the brush-ability of a brand, since some glazes of the same brand might be good for brushing while other might not.  

Amaco’s non-toxic F line I found really hard to brush, but I’m not sure if the problem was that they were old and bacteria had decomposed the gum or if they are always like that. The Art series was nicer to use.

The same thing with Duncan and Mayco, some colors are better than others. Really opaque glazes tend to be more troublesome than the semitransparent ones, but the opaque glazes are the ones that usually achieve even solid colors and stay put when fired.  

Glazes with crystals are a really fun to use but tricky to apply and give quirky results.

It took me a long time to get the process right, and what works for somebody might not work for another. Some of the solutions that either work for me or for people I know:

-Using a watered down first coat, adding a small amount of water the glaze or wetting the tip of the brush in water before dipping it in the glaze.

-Adding some kind of gum/suspender like CMC/Xantham Gum…  but some people add other stuff like bentonite solution/ liquid dish soap/ Glycerin/ Ironing Starch…

-Fire a cone or two higher

The brush selection makes a big difference too… I like using really soft hair brushes. Some people prefer fan brushes.

I think the key is and being able to tell by sight the coat thickness and get an even coat that is not too thin so the color is even and not too thick to avoid pinholes/shivering etc...

Regarding what is food safe and what is not, I recommend that you read up on the subject and draw your own conclusions.  There are many chemicals that are not regulated that I rather not use. Also, a glaze that is labeled as non-toxic might not necessarily be durable.  Vinegar on a glazed bowl will quickly show you that after a couple of days… :) That’s why I mix my liner glaze.

What is microwave and dishwasher safe is another matter you might want to research…

Edited by enbarro

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Thank you so much for your very detailed advices!!

They are very helpful ... but it also squeezed a bit my hope to try it with another glaze.
So maybe I should stick with the glazes I have and try to figure out what I should do differently. It's a "house-made" glaze from a Pottery Company. I really like this glaze (bright colors, not runny, also nice with textured clay). It's only difficult for me to brush-on ... I struggle to brush it on smooth and even. When I try to smooth out the overlaps it starts to crumble and it looks more than a paste than a paint. I tried different firings, different brushes, using more and less glazes ... but I don't get rid of the little pits and some pins. It is labeled with Cone 06, but the company said it could be fired up to Cone 03.

A friend of mine uses the same glaze but has not this much problem with "Pits" ... but she is firing with a gas-kiln, my kiln is an electric (smaller size, 4,7 cubic, with two thermocouples).

We both fired the bisque to Cone 04 ... I used Medium-Slow over 11 hours. Mainly little things like ornaments, beads, small plates bowls & boxes ... not stacked to tightly.
She fires the glaze to Cone 06, no hold
I tried different firings:
Cone 05, no hold
Cone 05, 20 Min. hold
Cone 06, 10 Min. hold
Cone 06, no hold

The best result I had with the last firing (cone 06, no hold, medium, around 7,5 hours). But I don't see a pattern ... in the same firing some objects have only very few and tiny "pits" and next to it another object with "pits" all over (tiny, fine, not deep into the glaze, like poked with a needle). Sometimes at the vertical, sometimes on the horizontal surface. Sometimes underneath the plate, sometimes inside the plate.



I try to figure out what else I could do differently.
Maybe more differences by the amount of glaze ? .... it's difficult for a beginner to know what is a thin layer and what is a thick layer.
Or maybe the "Hold" ? .... my result was better with "no Hold", but by reading it seems most people give the glaze-firing a holding time.
Another reading from the internet: In a slow-firing setting, you may need to soak the kiln longer at maturing temperature to give the glaze a chance to heal itself. In a fast-fire you need to do the opposite, soak only long enough to melt the glaze but not long enough to allow bubbles to grow. But what would this mean in my case?

So brainstorming and trying & trying .... and keep the hope :)

Thanks again for your help!

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You’re welcome. I also had a hard time figuring low fire clay/glazes when I started many years ago due to the lack of information available then on web.

Is your friend using the same clay? Have you checked if she/he is applying the glaze in the same manner? Would he/she be willing to fire a small glazed bowl of yours and vice-versa?

There are several things that can be causing the problem, but if you say that the glaze looks like paste then most likely the problems is the glazes need a suspender/binder and maybe remixing. Does the glaze after a few days of being unused separates with water on top and a hard mass at the bottom?

You could try mixing a cmc or xantham gum solution. Cmc is an organic substance and spoils overtime, so mix small amounts (5mg to 1 pint of water is what I usually mix because I don’t use it often). Pour the glaze amount you are going to use in a bowl and add small amounts (few drops at a time) of the cmc solution until it brushed the way you want it.

Xantham can be found in bakery shops and online store like Amazon, if your local pottery supplier doesn’t sell it…

Big commercial glaze manufacturers use fungicide and the glazes keep they brush-ability better over time. You could search the archive for Neil Estrick’s posts. I think he was the one that explain this to me some years ago…

http://community.ceramicartsdaily.org/topic/5582-suspendersbinders-in-speedball-glazes/

Maybe buying one or two 4oz Duncan or Mayco glazes can help you figure out if that is the problem.

Most likely you need more practice brushing the glazes and maybe a new glaze source, but possible cause for the pinholes:

-The glaze application is too thick

- The glaze wasn’t properly mixed or the suspender/binders clumped up.

-The bisque had dust

-The glaze didn’t fully mature or didn’t had time to heal. Your thermocouple might be slightly off, you could try firing cone 05.

- The bisque wasn’t porous enough or to porous and that can make even application more difficult.

If you notice the bubbles in the unfired glaze coat, rubbing the bubbles with the finger can solve the problem.

You could also try adding some clear glaze to make the glaze more fluid. At one point I used to add 1:5 of clear glaze to Duncan’s downright white glaze to avoid pinholes.

Brushing the first coat up and down and the second side to side can help too. To ability to judge thickness comes from experience, making many small slabs or shallow bowls and systematically try all the brushing options could speed up the process of finding out a solution.

I slow ramp up because I single fire, don’t hold at top temp or ramp down my firings, just fire to a cone or two hotter (cone 04-02). That is a personal choice since I don’t have time to baby the kilns. I also apply most glazes using a single thick coat of slightly watered down glaze.

Focus on the small successes and keep trying until you sort it out… :)

Edited by enbarro

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Thank you very much for taking your time & give me further advice!

I'm sorry I should have stated it clearer. By comparing with "you-tube-presentations" the glaze seems to have just the right consistency of a glaze: light creme, no clumps, light running. I shake the jar before I open it ...it doesn't separate nor has it a hard mass at the bottom. I stir it well & often ... it really looks & feels perfectly by stirring .... my problem starts with the second brush-stroke, when I try to smooth out the overlaps it starts to crumble and the glazed objects look more than having a paste on it than a paint .... it just looks different with the "Spectrum Metallic", which shows a smooth and even surface also after 3 coats.

My friend uses the same clay, but she uses bigger brushes and maybe uses more glaze. My objects are smaller and I like to paint details and "picky-poke" (is this a proper English-wording?) around little areas. I don't know exactly, but there seems to be a huge difference between gas-kiln-firings and electric-kiln-firings, isn't it? I try to figure out what differences the glaze is going thru in a gas- and in an electric-kiln (sorry, weird wording)

I dust off the bisque, keep it under a box till they get into the kiln for the firing. The witness-cones bent perfectly. I also checked my notes & pics ... the most worst objects with "Pits" were not placed at the same spot in the kiln (some nearer of the spyholes, some further away .... some on the upper shelf, some on the under).

That's what's bothering me ... there is no pattern.

I also thought about the bisque maybe not being porous enough. I have the habit to smooth every area of the finished clay-object out with a damp brush. But shouldn't I have more other problems then ? Not that I'm looking for it , but I only have a few "Pins" & very few little "blisters". My biggest problems are the "Pits" (tiny, only on the surface of the glaze, not thru to the clay-body) ..... I thought the "Pit-Problem" is more a problem with the glaze ...  ? .. or maybe I have misunderstood it?

I also like to try your suggestion with other low-fire-glazes. You mentioned that you liked the color purple from Speedball .... I couldn't find a pottery supplier in my area who sells Speedball, but Amazon has it ... when I looked at the color-chart the Purple seems to have also some "pits". What was your experience with this glaze/color ? ... to what Cone did you fired it ? ... also no holding time ?

I really appreciate all your helpful advices & thank you very much for taking the time! :)
 

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It sounds to me like the glaze might need more binding (gum) material…  


https://digitalfire.com/4sight/troubleshooting/ceramic_troubleshooting_powdering_cracking_and_settling_glazes.html


‘’Add CMC gum to powdering glazes. In industry gums are standard practice, companies know how to deal with their side effects. But potters should be aware of the impact of using a gum. Like bentonite, it needs to be added during dry mixing. Gum is glue, it is very sticky, it hardens. Using gum is a crow-bar approach, a way of 'gluing' a glaze on the ware. Strangely gum also helps suspend. Gum burns away so it has no effect on glaze chemistry (although the decomposition can produce glaze faults like blistering and pinholing). One serious problem: gummed glazes dry slower and drip-drip-drip after glaze slurry pull-out. This can be compensated in most industrial processes, but can be a total pain in pottery. Experiment with the amount, try 0.5% to start. Add it as a gum solution to the water (deducting the amount of solution need from the water requirement). Commercial paint-on glazes often contain so much gum that the recipe contains zero-water (only gum solution and the dry materials).’’


https://digitalfire.com/4sight/material/cmc_gum_228.html


Personally I avoid using powdery glazes, adding a gum to a powdery glaze is a solution I use only when there’s no other option. Usually I just mix it with another glaze to make it brush well and then fix the recipe or buy/mix a different glaze. 


I’m inclined to think that the problem is the glaze and or the application. Not noticing a pattern in the firing also points to the glaze being the problem.

If your friend’s kiln is bigger it might have a different ramping curve, but if she’s not doing reduction probably the difference shouldn’t be that big. 


If you make a tile about 5 inches wide and progressively apply the glaze thicker as you move to the right (one thin coat on the far left, then two coats, then 3, etc.. then scratch with your nail to judge the thickness) you might be able to tell thickness needed and if the glazes is bubbling due to it being layered too thick. The bubbling in photo seems to look like what I’ve usually seen with powdery glazes applied unevenly or needs remixing or an opaque glaze applied too thick. 


https://digitalfire.com/4sight/troubleshooting/ceramic_troubleshooting_glaze_pinholes_pitting.html


My experience with speedball glazes will not translate to your clay and firing methods. I single fire terracotta (red) clay to cone 04-02 in 5.5-8 hours, no hold or slow cooling. It makes me guess that if the thermal expansion of the clay isn’t drastically different from the earthenware average, many glazes are not that finicky and should work great for you as well… 


My suggestion is to use whatever works best right out of the gate to avoid getting too frustrated. As you get more experience you’ll be able to make most glazes work and know which to avoid altogether. Maybe try whatever you can readily source at a good price.

If you are a visual learner, check with local friends, sit down with them and let them show and explain how they go about the process. Or check youtube…

https://www.youtube.com/watch?v=_85QWDsIa80

Many 'ifs' and guesses...  hope it still helps you in the search for a viable solution...
 

Edited by enbarro

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Thank you soo much for all that many helpful information!

I'll start with also trying other glazes .... testing my glaze with clearer differences of more and less glaze-application .... different firings ... and trying & testing again...

Your wordings that it did took you a long time to get the process right pushed me and brought back the energy to keep going .... and even if it may take a while to get rid of the problem each testing will teach me something new.

I really thank you for giving me so many ideas for further testings! :)

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I’m confident you’ll find a solution very soon. When I started most manufacturers where in the process of reformulating leaded glazes (which up to that point many where still considered and labeled  as food safe) to make them lead-free and for a while the new recipes were not very good for brushing. These days there are many good options. :) 

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