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troubleshooting glaze color without buying all of the glazes in the world....

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I'm very new to the game, and for a first project I set out to make a set of floor tiles.  After some thrashing I can now use porcelain slip (Seattle Pottery SP930 Swan) to cast tiles.  The resulting tiles seem to be ok after I send them off for ^04 bisque fire.

The current problem is glazing.  I played with some colors in the Mayco Stoneware family (too bright!), and decided I wanted the Amaco PC-48 (Art Deco Grean) and eventually a couple of other colors from the family.  The picture on their website suggested "slightly heavy" coating of the glaze.  I made some test tiles and sent them off for firing (^5).  

They came back not at all like what I expected.  I'm after the nice green with spots as shown on the glaze page and the sample tile in the shop, not the dark brown with hints of green I got.  My result is matte, and I expected gloss.  The closest result I can find looks like the picture on the Amaco site showing how the PC-48 looks on various clay bodies -- specifically on the Clay Body 11-M ("A-mix white stone ware").   The glaze looks better on other clay Amaco clay bodies, but they don't show my porcelain.

The hoped for effect is something like the right hand tile in the image here.  I got something more like the upper left cup here.



How do I troubleshoot this?

  • is this a bad clay-glaze pairing?  I am reluctant to change clay now that I have a system to cast my pieces, but I also don't want to buy lots more glazes looking for one that might work.  Does the idea of two clays being "similar" even mean anything here?  I don't know what SP930 actually is beyond the "recommended" porcelain from the Seattle Pottery store.
  • Did I fire at the wrong temp?  I just sent the tiles off to the local shop and asked for mid-fire and they said that was ^5.  Are there other variables here and do I need to bribe the kiln operator to be more specific?  go a little hotter?
  • Did I put the glaze on wrong?  Too thick?  Too thin?  Wrong phase of the moon?

I know there so many combinations of glaze, clay, and temp that I could spend a year just making test pieces, and at that point I will have a large collection of almost full jars of glaze and still not have my 20 sq ft of tile that I need.  Is there a search method I can use to find a similar glaze on this clay?

Please take a look at the attached picture and see if there is something obvious....or do I just need to buy more glazes and make more test tiles.  The two small rhombs have either 1 and 2 or 3 and 4 coats of glaze.  there is not much difference between 3 and 4.  The large rhomb has 3 coats.    tile edges are about 4" long.


PXL_20231031_001544424 (Large).jpg

Edited by Clay Wallower
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Lots of questions! Frustrating I know. You are right about the variables, they are infinite. Some folks here use Amaco glazes so I am sure they will weigh in. In the meanwhile pc 48 appears to fire gloss to semi gloss and yours is more dead matte which makes me wonder if it is under fired. Checking the Amaco website, they seem to fire these colors at cone 6, not cone 5 so there is a possible explanation for the matte. Additionally Amaco used to claim many of these glazes are float glazes so a fairly thick application was also needed to get things to float after they liquify. So more tests along the lines of firing to cone 6 and heavier application might be the ticket. Don’t forget to include waster or cookies for your test tiles unless you are very sure they will not run.

Edited by Bill Kielb
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On 10/31/2023 at 10:08 PM, Clay Wallower said:

They came back not at all like what I expected. 

This may be the single most eloquent statement to ever describe working in clay. Welcome to the experience, and I’m sorry in advance!

There’s always more testing involved in getting a specific, desired result, but the payoff can be worth it. I agree with everyone above about firing to a hotter cone to start with, and making multiple tests with varying layers of glaze to find your acceptable working range.

However if that doesn’t fix it, I do notice that the more green range of colours on the chart with the different clay bodies were on the more darker or speckled clays. You could try a light iron wash over your existing clay once it’s cast, rather than trying to switch clays. A-mix and your chosen porcelain slip are both very light firing, and I can’t think it’s entirely unrelated to your results. 


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