Jump to content
Sign in to follow this  
clay lover

Should This Glaze Fire Out Glossy?

Recommended Posts

I have been using this glaze for a while now, and rarely it is the satin matte that the recipe describes, but most firings it comes out really glossy.it is well behaved in the bucket and dependable, no running, fires out smoothly, a nice glaze, but not what I want.

The cones are the same every firing and the clay is, also. The Si-Al rating is 4.6-1. any suggestions, the satin is great, the glossy not what I want.

 

Neph sy 47

dolomite 10

ball clay 10

gerstly borate 23

tin oxide 5

zircopax 5

Share this post


Link to post
Share on other sites

In my short experience firing I have never had a glaze come out two different firings looking exactly the same. Sometimes they radically change.

 

Is this a cone 6 recipe?

 

A guess would be removing some of the GB, adding in a little more dolomite and maybe some zinc oxide.

Share this post


Link to post
Share on other sites

I'm sorry, yes it is a ^6. the witness cones are very close each time and the cooling has not changed. I only got the satin 2 times, from many firings but it is SO nice, I want to figure out how to get there again.

and the si-al rating indicates I should be able to get the satin regularly ??and the book it came from says it is satin-matte.

Share this post


Link to post
Share on other sites

Try adding a cooling cycle to your firing if you're not already. It should help to knock down the glossiness. It could be that the firings in which it came out less glossy were fuller loads, and therefore cooled slower. Some glazes are very touchy about cooling rates. I used to have one that was high gloss in a fast cool, matte in a slow cool.

Share this post


Link to post
Share on other sites

Try adding a cooling cycle to your firing if you're not already. It should help to knock down the glossiness. It could be that the firings in which it came out less glossy were fuller loads, and therefore cooled slower. Some glazes are very touchy about cooling rates. I used to have one that was high gloss in a fast cool, matte in a slow cool.

 

Are there certain temperatures you want to slowly cool through? How much slower? 

Share this post


Link to post
Share on other sites

I cool at 175F/hr from cone 6 down to 1550F, because some of my glossy glazes look better with a little more time at the high end. Most people who slow cool will let it cool naturally to around 1950F, then slow cool down to 1450-1550F at 150-200F/hr, where matte glazes will develop.

Share this post


Link to post
Share on other sites

educate me, I thought the si-al ratio of 4.6:1 would have to produce a satin or matt. that is the ratio according to Hyper Glaze.

 

No, this is not a clear, it is a white and on white clay it looks like a toilette, but on browns is very nice, but very shiny.

Share this post


Link to post
Share on other sites

Thanks for the remix suggestion. Is there any way to try that with some of the the existing bucket?  I'm not the best with the glaze math.

 

You could weigh the same volume of glaze and water then subtract the waters weight from the glaze weight.  This will get a good estimate of how much dry glaze is in there.

 

Split up 1L into 100ml volumes and have 10 test glazes. The amount of dry glaze will likely be around the 50g mark in 100ml so you will need some exact scales as a 1% addition will be 0.5g of oxide. 

 

I don't think this would be very exact, depending on how accurately you measure the volume. Easier to make up new tests.

 

About the Si/Al ratio, I would think that you could be fluxing the Al into the glass.

Share this post


Link to post
Share on other sites

I would just mix a new batch.  Figuring out how much dry material is in a glaze mix is far more effort than it's worth and doesn't turn out to be all that precise. I tried to do it once and made a mistake in my math and ruined the whole batch--both new and old materials.

 

Keep the old batch for now, make a new one, test fire it on some tiles, and if you've got an undesirable result, you've still got the old, predictable batch around.

Share this post


Link to post
Share on other sites

For a  cone 6 glaze the recipe you gave doesn't have enough silica to be within the limits, the glaze doesn't add up to 100% and the fluxing power is very high so it could easily be glossy, the COE is also high which will cause problems on some clay bodies.  That is why a Currie 35 grid test is helpfull, and probably will show several good glazes.

David

Share this post


Link to post
Share on other sites

For a  cone 6 glaze the recipe you gave doesn't have enough silica to be within the limits, the glaze doesn't add up to 100% and the fluxing power is very high so it could easily be glossy, the COE is also high which will cause problems on some clay bodies.  That is why a Currie 35 grid test is helpfull, and probably will show several good glazes.

David

 

 

Matte glazes generally don't fall within limits.  That was a big lesson for me in 2014.  Limit formulas are mostly for glossy glazes for functional ware.

Share this post


Link to post
Share on other sites

John posted a good explanation a while back about glazes and limits.

 

 

It all depends on that for which you are looking.

 

The most "interesting" glaze surfaces typically are those that come from some so-called 'imbalance' in the oxide distribution in the melt, most often causing some chemical unevenness in that melt, the lack of full melting of some raw material component, or the precipitation of some silicate type materials onto the surface in the cooling phase.  Or all of the above.  Or takes advantage of a raw material source for oxides that casues a 'defect' as the glaze is melting ... that we look at as "nice" (ie. American Shino crawling). 

 

Keep in mind the "limits" that everyone talks about are for what might be defined as "good glass".  And that "good glass" is defined by relatively modern industrial standards. The criteria has as much to do with stability, REALLY long term durability, and consistency as it does with any aesthetic qualities.  THOSE are criteria for mode rn industry.  (There is a reason that bathtub and toilet and sink glazes look like they do.)

 

If you are not concerned about the same things...... then the "limits" can apply less and less to what you are doing.

 

If you are making food service wares....... then concepts like the leaching of potentially toxic materials likely should be in your list of desired criteria. 

 

If you are making sculptures for outdoor installations, then stuff like durability in acid rain and pigeon poop likely should be in your list of desired criteria. 

 

If you are making floor tile, then hardness and resistacne to abrasion likely should be in your list of desired criteria.

 

Understanding how the various limit formulas might help you evaluate your list of personal criteria is where the art of USING glaze chermistry software comes in. 

 

Only you can decide what those criteria are. 

 

The only formal "laws" relative to the production of ceramics in the USA at the moment are from the FDA and the State of California... and they pertain to any wares that contain lead or cadmium compounds.  Not hing else is formually regulated.  You also DO have what are known as standards from organizations like ASTM for the labels of things like "microwave safe" and "dishwasher safe".  Of course general liability law says if something you make harms someone... you can be held liable in either civil or even potentially criminal (unlikely) situations.

 

Then there is a piece that is the "moral" dilema.  If you make wares that are somehow "sub-standard" in some way....... and you know that they are....... what do you do with them?  For example, if you have a dinnerware glaze that is drop dead gorgeous........ has NO toxic components...... but it is outside limits.... and the way it is outsisde those limits tells you that compared to a piece of commercial Noritake dinnerware....... the surface will not stand up to repeated washings as well......... what do you do?

 

NO easy answers.

 

Anyone who uses American Shino and sells it is "outside limits".  (Guilty!)  Anyone who woodfires and sells work with natural fly ash deposits is "outside limits".  (Guilty!)

 

best,

 

........................john

 

Share this post


Link to post
Share on other sites

 

For a  cone 6 glaze the recipe you gave doesn't have enough silica to be within the limits, the glaze doesn't add up to 100% and the fluxing power is very high so it could easily be glossy, the COE is also high which will cause problems on some clay bodies.  That is why a Currie 35 grid test is helpfull, and probably will show several good glazes.

David

 

 

Matte glazes generally don't fall within limits.  That was a big lesson for me in 2014.  Limit formulas are mostly for glossy glazes for functional ware.

 

You are correct.  Michael Bailey in "Glazes cone 6" states that alumina matte glazes are temperature sensitive  and plus minus 50 deg F can make them matt or shiny. So maybe if the witness cones are not the self standing type

there could be a temperature difference that regular cones wouldn't show?

David

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
Sign in to follow this  

×

Important Information

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