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Are Coyote Clear and Amaco Underglazes incompatible?


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#1 Pugaboo

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Posted 27 April 2013 - 04:55 PM

I did up several of these small Pug shapes to make a windchime ALL of them bled as shown in the photo. Neither I nor my teacher know why and he even called Coyote but all they would say is if I did not use their underglaze with their clear glaze they can't say why the colors bled. Also if you look closely at one of the images it almost looks like the clear glaze has a bunch of tiny bubbles trapped in the glaze along the bottom edge. The color of the suntan body also has a greenish cast to it which when I used it before it did not have.

Clay- Little Loafers
Underglaze Amaco LUGs - Suntan for the body color and black detail lines painted on during greenware stage then bisque fired to cone 04
Glaze - Coyote Clear - dipped then glaze fired to cone 6 on a bead rack hanging vertically

Has anyone out there used this combination and had an issue with bleeding? The underglazes were bisque fired so shouldn't they have been permanent after that stage? Did this happen because I used Amaco underglazes and coyote clear?

I'm trying to understand what I did wrong so I can adjust my process and get better results next time so any help would be greatly appreciated.

Terry

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#2 Nancy S.

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Posted 27 April 2013 - 07:17 PM

I did up several of these small Pug shapes to make a windchime ALL of them bled as shown in the photo. Neither I nor my teacher know why and he even called Coyote but all they would say is if I did not use their underglaze with their clear glaze they can't say why the colors bled. Also if you look closely at one of the images it almost looks like the clear glaze has a bunch of tiny bubbles trapped in the glaze along the bottom edge. The color of the suntan body also has a greenish cast to it which when I used it before it did not have.

Clay- Little Loafers
Underglaze Amaco LUGs - Suntan for the body color and black detail lines painted on during greenware stage then bisque fired to cone 04
Glaze - Coyote Clear - dipped then glaze fired to cone 6 on a bead rack hanging vertically

Has anyone out there used this combination and had an issue with bleeding? The underglazes were bisque fired so shouldn't they have been permanent after that stage? Did this happen because I used Amaco underglazes and coyote clear?

I'm trying to understand what I did wrong so I can adjust my process and get better results next time so any help would be greatly appreciated.

Terry


I've used Coyote's clear with Amaco Velvets, but not with fine lines so I can't attest to the bleeding issue; however, I know the bubbles (which I also get with Amaco HF9, their zinc-free clear) as well as the not-quite-clearness of it (also an issue with Amaco HF9). I'm not sure if the LUGs need it, but the Velvets require a Zinc-free clear -- and I asked Coyote if it was zinc-free, and they said it was.

On a white claybody, they are both slightly ecru. On a suntan body, with black underglaze bleeding around....well, that would explain the greenish cast. Black underglaze sometimes looks greenish when diluted.

As for the bubbles, I'm not sure how to fix that. I noticed mine where the glaze was layered thickly where a mug handle met the mug, and if yours were along the bottom edge, it's likely due to the glaze running and collecting thicker at the bottom during firing.

My only thought about how to avoid the bleeding is to underglaze, fire, then add the clear glaze and fire again.

It's too bad the underglaze ran -- those are really cute!! Good luck!

#3 bciskepottery

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Posted 27 April 2013 - 07:26 PM

Your underglaze colors are not permanent after bisque; in the glaze firing, they remelt . . . and at a higher temperature. The bleeding could be a chemical reaction between the clear glaze and the underglazes; it could also be a case of gravity . . . as the clear melts in the glaze firing, it will flow downward since the pieces are suspended by wire.

You could try an Amaco clear and see it you get the same results. You could try Coyote underglazes with the Coyote clear. You could also bisque the chimes (with underglaze applied) to cone 6, then apply a low-fire glaze and glaze fire at that temperature. If vitrification is not an issue, then you could bisque with underglazes and then apply a low fire glaze and refire them in another bisque load.

#4 Diane Puckett

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Posted 27 April 2013 - 07:54 PM

It also looks like there are pinholes in the dark blue areas, unless that is just the photos. I have not used this combo. For what it's worth, I have used Opulence Clear Liner Glaze a lot in the last few years with absolutely no problem other than a little running when I got it too thick on a large sculptural piece. It is more satin than gloss. I had problems with pinholes in multiple glazes on Little Loafer. The same glazes on B-Mix are fine.

I love your little dogs. They fit right in with antique flow blue pottery.
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#5 Pugaboo

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Posted 27 April 2013 - 09:43 PM

Nancy- yes the LUGs state some colors need to have zinc free clear used as well just like the Velvets. I too called Coyote and they said their clear was zinc free. I will try doing up one and brush on a coat of the Amaco zinc free clear since i think i can get a thinner coat that way and see how that goes. When you say underglaze fire clear glaze and fire again do you mean to apply underglaze during greenware the bisque fire AND glaze fire it at cone 6 THEN apply the clear glaze and fire again at cone 6?

Bciskepottery - I will take what you said into consideration. I will also test by firing one laying done on a stilt to see if its the vertical aspect that is causing the issue. Since these are for wind chimes not food items I don't think vitrification is essential so if the tests come back showing the same faults I will try the underglaze applied and fired to cone 6 then a low fire glaze to what is now the bisque fire temp of cone 04 instead. Which brings up a question do you HAVE to apply a glaze over the underglaze? What if i just apply the underglaze and fire to cone 6 would the clay vitrify and make itself water proof without the use of a covering clear glaze? The windchimes are meant to be hung outside on a porch so there is the chance they could get wet. What do you think?

Diane- Yes there are small pinholes in the black areas but none in the suntan areas. Is Opulence the name brand? I have been shopping at Clay King primarily and don't see a brand by this name. I do not own my own kiln (yet) but am a member of a group studio so I am limited by the studios rules. I have to use the clay they sell (little loafers is one of them) and I also have to fire at cone 04 and/or cone 6. They also prefer that either Amaco or Coyote brand glazes be used but with glaze brands have a bit of leeway if I tell the director I am using a different brand and do some tests using bisque trays under items in case they run badly to protect the shelves.

Thank you all for saying you like the little dogs, I have every intention of figuring this out and can hopefully show you a successful set shortly. Lots of things to consider and test out. Any additional suggestions are welcome!
The world is but a canvas to the imagination - Henry David Thoreau

#6 bciskepottery

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Posted 27 April 2013 - 11:19 PM

No, glaze over the underglaze is not necessary. Just fire the piece to cone 6 (for Little Loafers) and the clay will be vitrified. Clay fired to its virtified cone does not need glaze to be water-tight or water-resistant.

#7 weeble

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Posted 28 April 2013 - 03:22 AM

You'll get a sturdier windchime by firing to vitrification, otherwise the chimes are much more likely to chip.

That and they sound 'duller' if not fired all the way up!
Maryjane Carlson

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#8 Diane Puckett

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Posted 28 April 2013 - 06:47 AM

Opulence is the brand. I buy the dry mix and then mix it with water and sieve it.

When you make wind chimes, always make extra pieces. It is common for them to break in high winds, and it is nice to have replacement pieces ready to go.
Diane Puckett
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#9 OffCenter

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Posted 28 April 2013 - 08:47 AM

If the sound is important to you, you should test a lot of clays before using one. There is a huge difference. A glassy porcelain fired to full maturity has a much better sound than most stoneware clays, especially heavily grogged ones. Glaze usually dulls the sound. Thinner pieces almost always have better sound, but, of course, the thinner the pieces are the easier to break. Shape affects the sound, too. The most important thing to do is fire the clay to maturity or a little beyond (and as we all know you have to find where that is by testing, not reading what the manufacturer claims). If you insist of glazing the pieces, spraying a thin coat on is better than putting a muffling gob on by dipping.

Jim
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#10 Nancy S.

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Posted 28 April 2013 - 09:48 AM

Nancy- yes the LUGs state some colors need to have zinc free clear used as well just like the Velvets. I too called Coyote and they said their clear was zinc free. I will try doing up one and brush on a coat of the Amaco zinc free clear since i think i can get a thinner coat that way and see how that goes. When you say underglaze fire clear glaze and fire again do you mean to apply underglaze during greenware the bisque fire AND glaze fire it at cone 6 THEN apply the clear glaze and fire again at cone 6?


Definitely try a thinner coat, if you plan to glaze them. I think I like the idea of not glazing and just underglazing the lines and having a matte finish - the sound may be better as well if you do that.

bciskepottery's right about the gravity -- and about the remelting. I was thinking that part of the "running" of the underglaze happened when you dipped the chimes into the glaze initially, so if you were to underglaze the greenware, bisque, glaze, do the glaze firing, it might not run *as much* but it may still run. Not sure!

Keep us posted on what you decide to do... Posted Image

#11 nairda

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Posted 28 April 2013 - 05:15 PM

Have used both Amaco Liquid Underglaze and Velvets with no running beneath clear glazes. Used Highwater Little Loafers. Under glazes applied to leather hard clay, bisque to cone 06. Used either of the clear glazes found in Mastering Cone Six Glazes. Fired to cone 6. Line work stays put, but most of it is on horizontal surfaces.

#12 neilestrick

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Posted 29 April 2013 - 10:29 AM

Underglazes can respond differently to different clear glazes. It'll take some testing. Remember that most underglazes are not formulated for cone 6, so some discolor, some bleed, some are fine. Speedball underglazes work great at cone 6.
Neil Estrick
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