Clear glaze recommendation?

[hlipper]

Hi folks - looking for a clear glaze recommendation to use on my speckled white stoneware. My current Mayco clear is not working out on that clay body (because of the speckles). Thanks in advance!

[Min]

5 hours ago, hlipper said:

My current Mayco clear is not working out on that clay body (because of the speckles)

Not sure I'm understanding what's going wrong with the clear on the speckles? You want the speckles to show or ?

Welcome to the forum.

[hlipper]

7 hours ago, Min said:

Not sure I'm understanding what's going wrong with the clear on the speckles? You want the speckles to show or ?

Welcome to the forum.

Thanks! So I've noticed the Mayco clear creates a lot of bubbling on speckled clay. I also spoke with a tech there who confirmed their glazes are suited for non-speckled white stoneware. Let me know if you have additional questions!

[Min]

Haven't heard or read that Mayco clear isn't compatible with speckled clay so not sure what's going on. Post a picture and give some firing and clay details, might help sort it out.

I don't use commercial glazes so can't recommend one, @LeeU, @JohnnyK or anyone else who uses commercial glazes, have you run into this issue?

 

[hlipper]

2 hours ago, Min said:

Haven't heard or read that Mayco clear isn't compatible with speckled clay so not sure what's going on. Post a picture and give some firing and clay details, might help sort it out.

I don't use commercial glazes so can't recommend one, @LeeU, @JohnnyK or anyone else who uses commercial glazes, have you run into this issue?

 

Sure thing - Pieces are slow bisqued at ^04 and slow glaze fired at ^5. My white stoneware is dark star from mudworks: https://kymudworks.com/collections/ky-mudworks-clay/products/dark-star-5-7?variant=29151550013519 

and the brown stoneware is from ceramic shop: https://www.theceramicshop.com/product/859/speckled-brown-clay-112/

this is the clear I've been using: https://www.theceramicshop.com/product/10873/clear-one-dipping-3-gallons/

Thanks!!

[Min]

Thanks for posting the pictures. Looks like the manganese speckles are offgassing enough to create the blisters and bubbles but the glaze isn't smoothing over.  Think the slow bisque you are doing isn't slow enough at certain temperature ranges of the firing. Have a look at the bisque firing schedule from Steve Davis link below. There are critical ranges that need the heat to go slowly at. Organic carbons burn out from 300-600F, inorganic carbons from 1290-1650F and sulfurs between approx 1300 - 2100F. So for the bisque I'ld slow it down during those ranges, especially the one for inorganic carbons, wouldn't hurt to add a soak at around 1500F either.

Changing the glaze isn't going to stop the problem of the clay offgassing.

https://ceramicartsnetwork.org/wp-content/uploads/2018/06/bisque-firing-schedule.jpg

 

[hlipper]

Wow, I would have never guessed. Thanks so much for the insight! I'll check out that schedule for sure. Thanks again, much appreciated!!

[hlipper]

On 6/29/2021 at 4:04 PM, Min said:

Thanks for posting the pictures. Looks like the manganese speckles are offgassing enough to create the blisters and bubbles but the glaze isn't smoothing over.  Think the slow bisque you are doing isn't slow enough at certain temperature ranges of the firing. Have a look at the bisque firing schedule from Steve Davis link below. There are critical ranges that need the heat to go slowly at. Organic carbons burn out from 300-600F, inorganic carbons from 1290-1650F and sulfurs between approx 1300 - 2100F. So for the bisque I'ld slow it down during those ranges, especially the one for inorganic carbons, wouldn't hurt to add a soak at around 1500F either.

Changing the glaze isn't going to stop the problem of the clay offgassing.

https://ceramicartsnetwork.org/wp-content/uploads/2018/06/bisque-firing-schedule.jpg

 

Hi again! I followed the schedule you sent (the only change was I held for 2 hours vs. 12 hours as my pieces were dry and fairly thin). but unfortunately I had the same exact outcome with the bubbling (pieces look just like pics above). Any other thoughts? Thanks in advance!!

[Hulk]

I've had some improvement (with fizzing - very small bubbles) from extended holds at ~1500F in the bisque fire, both up and down, with powered kiln vent supplying a trickle of "fresh" air, adequate oxygen being important, so the authorities say (powered kiln vent also really helps reduce the fume load in the studio; I've set up a hood with a 400cfm to catch most of the rest as well as most of the waste heat as well...).

Other adjustments for the fizzing red and black clays (I'm no longer buying black clay, but will continue with red!):

 i) drop and hold in glaze schedule - drop from peak temp to 100F below peak, hold there for an hour, then slow drop to 1850F before turning off the heat and powered vent

ii) lower peak - I'd started out shooting for a cone 6 bent alla way over, now I'm shooting for cone 5 bent to "proper" position for red and buff clays.

iii) bubble clearing glaze - some glazes clear the bubbles better than others; for clear, I've found Wollastonite Clear works fairly  well. The few colours I'm using all behave fairly well.

Here's a start on background/related info, which may be helpful, tmi, or somewhar in between...

Drop-and-Soak Firing (digitalfire.com)

Blisters (digitalfire.com)

Surface Tension (digitalfire.com)

[Min]

1 hour ago, hlipper said:

but unfortunately I had the same exact outcome with the bubbling (pieces look just like pics above)

I'ld contact both KyMudworks and Standard and ask them what they recommend. Since you are using commercial glazes it might just be a case of trial and error. I'ld stick with the really slow bisque until you get the problem sorted out, it might not be necessary but removes some of the variables. Do you only use clear glaze or have you had success with other glazes for these claybodies?

[hlipper]

On 7/7/2021 at 11:18 AM, Min said:

I'ld contact both KyMudworks and Standard and ask them what they recommend. Since you are using commercial glazes it might just be a case of trial and error. I'ld stick with the really slow bisque until you get the problem sorted out, it might not be necessary but removes some of the variables. Do you only use clear glaze or have you had success with other glazes for these claybodies?

I reached out to Mudworks and their staff said they actually had the same issue with that Mayco clear. They said some folks have had luck with a 20 min hold during glaze firing but ultimately recommended switching out to another clear. My other glazes have worked well on the clay bodies (aside from Mayco's white gloss which I'm told does not work with speckled clay bodies). Interesting.

[Min]

Thanks for the update, good to know. You could try the drop and hold/soak @Hulk linked to but it could well turn out to need some tweaking of the schedule. Seems Mayco should address this issue given speckled clays are so popular right now.

I haven't used it on speckled clay and don't know if it fits your claybodies but Lagunas MS29 is a really nice clear. It's a cone 5 glaze but I used it at cone 6 about 25 years ago and it was fine. It did settle and hardpan really quickly back then, don't know if they have addressed that issue, if not, some epsom salts solution will take care of that if you try it.

[hlipper]

On 7/9/2021 at 2:18 PM, Min said:

Thanks for the update, good to know. You could try the drop and hold/soak @Hulk linked to but it could well turn out to need some tweaking of the schedule. Seems Mayco should address this issue given speckled clays are so popular right now.

I haven't used it on speckled clay and don't know if it fits your claybodies but Lagunas MS29 is a really nice clear. It's a cone 5 glaze but I used it at cone 6 about 25 years ago and it was fine. It did settle and hardpan really quickly back then, don't know if they have addressed that issue, if not, some epsom salts solution will take care of that if you try it.

Agreed, need to reach out to Mayco again but I tried Mudworks' super clear and it was great (just pulled this pieces out of the kiln this morning). No more bubbling. I'll check out your recommendation above as well. Thanks!!