Jump to content
tbaa

making my glazes and failing

Recommended Posts

Can someone help me resolve glaze problems please?  Several firings and tests later,  I am still unable to get a good base glaze.  Yes, new at all this,.  Besides  working in a remote area in the mountains in  India.  Some of the materials have been  a problem.   I paid for a ceramicist specializing in glazes to  come to  help.     After two weeks of work, I have one glaze base that works, but still needs to go to 1265C.  NOT the cone  6 I wanted.   I have about 8 base recipes that are of NO use to me  ;).  They all need to go to 1280C -   Now that I know my  potash feldspar was defective, I will try Nelsons Base etc all over again.  But would love to have this one recipe work at ^6.

Could anyone suggest  how to adjust  it??  (The minimum this glaze needs is 1250C - and can go to 1280+.  so I am pretty sure i wont get the melt I need at 1222C. ) Ingredients are:   Soda Feldspar 45;  China Clay  20;  Dolomite 20;  Talc 5;  Whiting   3;  Titanium  5;  Tin oxide 2.    I get a nice slightly speckled grey.  Some test tiles were more creamy than grey, but wares all fired as grey.  Cobalt and red iron oxide have worked well.  Copper has not.  

Any ideas of what other colorants to test with the above, or why copper didnt work ....?  That is IF there is a way to make this a cone 6 recipe???  Sorry to sound so ignorant - but chemistry is a beyond my scope - :(  Doing ma best - but mainly trial and error.  I do NOT understand the what, how and why of the materials !!  I LOVE my bisqued pieces.....^_^  

Share this post


Link to post
Share on other sites

Not a chemist nor an accomplished potter. However, I keyed the recipe into glaze software. The silica is very low, magnesium is a bit high. These are according to Roy-Hesselberth target.

Others with more experience should chime in.

 

Share this post


Link to post
Share on other sites

@tbaa, what other ingredients do you have available? Can you get silica and any other fluxes, anything that contains boron? Also, are you looking for a glaze to go on functional pots? What type of kiln are you firing in?  Any other details on the soda feldspar and china clay, do you have the supplier names for those or is that all the information you can get?

Share this post


Link to post
Share on other sites

It's high in magnesium, low in silica. If those are the only materials you have available, try this:

Soda Feldspar  41

Whiting  18

Dolomite  7

China Clay  11

Silica  23

It should melt at cone 6. If you have access to a boron frit, add it to your original recipe in 3% increments and it'll eventually melt at cone 6.

Share this post


Link to post
Share on other sites
1 hour ago, High Bridge Pottery said:

Not sure adding silica will help it melt. 

 

 

The original recipe had a really low Si:Al ratio, 3.7:1. There wasn't enough silica to make a stable glaze, probably not enough for the fluxes to work on. I simply put some of the magnesium into the calcium, and gave it enough silica to have something to work on. Put it into a limit formula and it works at cone 6. It's a little high in calcium, and may still need a little more silica, but it's a good start.

Share this post


Link to post
Share on other sites

How wonderful to wake up to so many replies.  I will call my supplier today and get details on the feldspar.. I have 4 different frits - equivalents of Ferro 3195,  3134,  (which I believe is a 'boron frit",)  3124 and 3110.  These are sold under the manufacturer's 'code', and some of the ferro frits are grouped /lumped together as one.   (Ferro 3110, and 4110 are sold  as one.  Ferro 3134, 4108, 4144 are grouped as one.)  I have both 3134 and 3124 which are labeled as Calcium Borate frits, and have the same temperature references.  I dont know what makes them different, but I have smaller quantities of these.  I also have lead bisilicate which the glaze guy wanted, to demonstrate how well it melts.    I have wollastonite, talc, whiting, gerstley borate, zinc oxide, dolomite, strontium carb, lithium carb,  in varying quantities.  I think these are all fluxes .  A host of other materials - oxides, opacifiers etc - neph sye, ball clay, china clay, EPK/Kaolin and even 2 kilos of cornish stone.  

I fire a gas kiln.  After about 6 glaze firings, I finally felt I had some sense of the workings of my kiln yesterday.  Cone pack at the bottom melted before the cone pack on top.  And cone 5 did not melt at the temperature it should have......or the temperature gauge is defective.....

 Neil, I will certainly test the recipe you suggest.  And glazenerd, I will check with the supplier if Mahavir potash spar is available here.  (You will be amazed at what India exports and what is available for local consumption.....)  I had 20 kgs of Potash feldspar, which turned out to be the main defective ingredient  - most of the glazes I was tested were coming out dry.   Apparently it was for very high fired glazes, or completely defective.   When the glaze guy made his first batch, they were all bad.  Shocking for him, no surprise for me - and he would not look at the results of my material tests before mixing his recipes.  I had to dispose of the potash spar, and have used only soda feldspar for my new experiments.

Thank you all so much.  

Share this post


Link to post
Share on other sites

Yes, most things are available, but the quality is uncertain.  And being new at this, I have no way of telling what it should be.  I would like matte glazes.  Yest, the original is matte, though the pieces near the flame were quite glossy.  

 I quit trying reduction  as the glazes werent working, and I figured getting the hang of kiln and the firing process  should come first.   (1st time i've fired this kiln with some sense of control....)  so maybe I'll try reduction after I get my glazes set up.

Everything came out great today - again a first!  The Amaco glazes (i have a couple of jars) work well consistently.  Indigo blue float for example.  So I do think the materials have something to do with the results.  

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×

Important Information

By using this site, you agree to our Terms of Use.