Jump to content
Sign in to follow this  
oly

What Causes Glaze/clay 'tide Mark'?

Recommended Posts

It is volatile compounds in the glaze are fuming the body along the border.  The common factor in the neph sy and the wood ash fusion buttons is high levels of sodium.  Potassium also does it.

 

You can't see the same stuff coming out of the larger expanses of the glaze surface and going into the kiln atmosphere... because it won't "mark" the glaze surface it is coming from.  But the bare body acts as a "tracer" for this stuff.

 

Almost all high wood ash glazes do this.  Ditto to high soda ash shinos.

 

Less common at cone 6 range than at 9-10 due to the reduced volatility of the soda and potash compounds.

 

best,

 

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

drmyrtle and oly like this

Share this post


Link to post
Share on other sites

I bought a pot in Cornwall a few decades ago, which appears to have a dolomite glaze over white stoneware body.

Interestingly it seems to have not a tide-mark but significant areas of the browny-orange.

post-34897-0-07771000-1425295919_thumb.jpg

 

Looked at more closely the areas appear speckled but free from edge-effects.

post-34897-0-20577600-1425295974_thumb.jpg

 

Any ideas what's happening? I go along with the solubles/volatiles theory for the

previously described tide-marks. Perhaps the pot was dipped and finger-wiped,

distributing the solubles uniformly over a significant [unglazed] area?

 

PS Chris your example seems to show both tide-marks and more solid areas. Would

you like to comment on any differences in treatment?

http://community.ceramicartsdaily.org/topic/7948-what-causes-glazeclay-tide-mark/?do=findComment&comment=76296

post-34897-0-07771000-1425295919_thumb.jpg

post-34897-0-20577600-1425295974_thumb.jpg

oly likes this

Share this post


Link to post
Share on other sites

I have this happen regularly with high gloss glazes on  higher iron content stoneware, especially in areas where the glaze is thinner (like one dip instead of two).  Like others have said, that level of happy accident is something we celebrate (and try to duplicate)...if you can actually get to the point where you can actually control it with any level of predictability, please let us in on the secret!

 

-Paul

oly likes this

Share this post


Link to post
Share on other sites

I bought a pot in Cornwall a few decades ago, which appears to have a dolomite glaze over white stoneware body.

Interestingly it seems to have not a tide-mark but significant areas of the browny-orange.

attachicon.gif_vase_cropped_10cm.jpg

 

Looked at more closely the areas appear speckled but free from edge-effects.

attachicon.gif_vase_detail_10cm.jpg

 

Any ideas what's happening? I go along with the solubles/volatiles theory for the

previously described tide-marks. Perhaps the pot was dipped and finger-wiped,

distributing the solubles uniformly over a significant [unglazed] area?

 

PS Chris your example seems to show both tide-marks and more solid areas. Would

you like to comment on any differences in treatment?

http://community.ceramicartsdaily.org/topic/7948-what-causes-glazeclay-tide-mark/?do=findComment&comment=76296

 

That looks like the colour of the clay body to me. Are you sure it is white stoneware? What colour is it on the bottom?

Share this post


Link to post
Share on other sites
That looks like the colour of the clay body to me. Are you sure it is white stoneware? What colour is it on the bottom?

 

White.

 

 

post-34897-0-32436900-1425302272_thumb.jpg

 

 

PS Note that the tide-mark at the bottom edge is not very pronounced.

post-34897-0-32436900-1425302272_thumb.jpg

Share this post


Link to post
Share on other sites

The finger wipes are thinning the residual glaze coating on top of the body.  This thin glaze coating is on a stoneware type body, so the interaction of the glaze and clay body (called the interface zone) will exist.  This is where the body grows crystalline materials into the glaze, and the glaze "eats" materials out of the body. 

 

In this situation there is little glass forming there... and the percentage of the body materials that are "in" the super thin glaze layer is high relative to the glaze's normal composition.

 

Two things are happening there.  One is that the alumina from the body is raising the Al2O3 content of that glass there.  That will tend to influence color rendition out of any oxides present.  Secondly, even white stonewares contain traces of iron oxide. 

 

The combination of a high alumina glassy phase and small amounts of iron oxide cause iron to go to the reddish color phase.  Hence the reddish brown marks. 

 

Same reason real shinos blush with that red firecolor on the thin spots on the high alumina refractory bodies they use.  Difference her is the presence of calcium and magnesium...... which dull the iron colors more toward the browns.. 

 

best,

 

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

High Bridge Pottery likes this

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  

×