Jump to content

Recommended Posts

Hello -

For many years I’ve been using Amaco’s Jet Black underglaze on white stoneware, firing to ^05/04 bisque and it’s always behaved really well. I recently started a new gallon bottle, mixed it up in a bucket really thoroughly before using. It was pretty thick, and I diluted it somewhat. I apply the underglaze to greenware in order to do sgraffito. Now I’ve started to see crazing when the bisqued ware is dampened - when sponging prior to applying clear glaze, and then much more noticeably when applying glaze (typically Amaco’s HF-9). Picture below. Although I’d already diluted the underglaze, it happened again with the next bisque. The folks at Amaco couldn’t account for it. I’ve been nervous about possible problems firing these pieces to ^5/6, which I’ve always done in the past - I don’t know if that would be risky. Any suggestions out there? Thank you!

01818499-964E-481E-8911-BB7F94B0CB18.jpeg

Share this post


Link to post
Share on other sites

That's not crazing, that is where it has cracked while shrinking.  I am going to guess you added a little too much water?  It would cause it to shrink even more than normal while drying.  Try evaporating some water off or adding more layers.  Crazing is when glaze cracks after firing due to a poor fit.  You should mix to the directions and then use a deflocculant to make it juicier.

That's just what it looks like to me

Edited by liambesaw

Share this post


Link to post
Share on other sites

Thank you so much for such a speedy response and for this explanation. Would a few drops of gum help? And how do you think it would fare in a glaze firing? I have visions of the glaze popping off and causing havoc...thanks again

Share this post


Link to post
Share on other sites

I think just leave the lid off the bucket for a day or two, get some of the water out of it, if it's too thick for you after that, add a few drops of sodium silicate to thin it instead of water.  That is, if that's the issue.  Might wait for someone else who knows more about underglaze to show up.  I dont think gum will help with anything other than brushability.  

I think if you can rub it off now, it won't be a good idea in glaze firing.  If it appears to be well adhered, should be good to go.

Share this post


Link to post
Share on other sites

I would guess an underglaze problem. I’ve never been able to thin so much that it cracks especially to that level of separation. Even when I airbrush with underglaze. Almost as if the underglaze is missing an important binder agent. Maybe I am mistaken but the clear lines are your sgraffito and the remaining separations are the underglaze issue. 

Share this post


Link to post
Share on other sites

Hello - thank you for your response. Yes, the long vertical lines are my sgraffito and everything else happened naturally! I’m inclined to agree that it might not be a question of being too thin, as I’ve used thinned underglaze in the past and not had this happen. I’ve been in touch again with Amaco, who haven’t explained the problem, but have seen it before and don’t predict issues in the glaze firing. They also say it isn’t because of too much water. I suppose if it is ok in the glaze firing, I don’t need to worry about it, but I still don’t like it!!

Share this post


Link to post
Share on other sites
12 hours ago, neilestrick said:

I would try adding some gum. Thinning them out shouldn't matter, they just go on thinner.

Right, since they make underglaze sets, that look like a watercolor paint tray.  They are meant to be applied quite thin, and used in a "painterly" way.  

I've also used the standard, bottled underglaze, and thinned them with water, when I'm blending a gradient, or something of the like,.  I've had no issues with either.  

I have had underglazes flake off before, but never crack, like that.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

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