Jump to content

Glaze Sinks In To Clay Body


Bob Coyle

Recommended Posts

Here is my sad story....

 

I teach a ceramics class at the local senior center here. I went to our only ceramic supplier to buy clay for the class but they were almost out of everything in the cone 05 range and would remain so till after the first of the year, so I bought some em-215 terra cotta. I have a whole lot of glazes I made up for the last classes and I did test tiles to see how they looked on the new clay... YIKES! they sunk in so badly that there was hardly anything left on the surface.

 

So what could I add to these glaze mixes that might keep it from sinking in so badly. Since this is a class for beginners we brush it on and fire it once. Brushing it on twice will not work . I always do a second coat on half my test tile, and it still sunk in. The class is coming up in January And I don't have time to do a lot of testing of a new glaze.

 

The basic recipe for glaze called “Jacky†is below.  I think came out of an old C.M.. It worked fine at cone 05 on two other clay bodies so I was not expecting the problem.

 

Jacky cone 05 glaze

 

Component           % Amt

Flint                         44.2

Gerstley borate        29.2

Nepheline syenite    11.5

Lithium carbonate   10.1

EPK                          05.0

 

plus 3% CuCo3 or 1% CoCo3 or 3% CrO or 3% RIO

Link to comment
Share on other sites

I suggest getting the right clay for your students no matter where you have to drive.Its just going to be better than reinventing the wheel in the 13 hour-for them and you.

terra cotta is just that and making it something else will be a slow time consuming process.

That is my secret I have learned over 40 years with clay passed on from the grand foba grinch of ceramic wisdom.

Many people want to use dirt and whatever and have it turn into gold but most find in the end its just dirt and a whole bunch of time and energy gone by.

This is how this may play out

 

 Went to a gas station  with a car full of students and they where out of gas so I filled the tank with water thinking it would work-well after the tow and draining the tank and new fuel all is back to the same only my passengers and wallet are both peed off.Turns out gas is what I really needed!

Mark

Link to comment
Share on other sites

I think you need to bisque much higher ..like ^02 then try glazing. Terra cotta matures higher than 02 usually., but it sounds like the bisque was too low. when doing majolica on terra cotta, I bisque that high before glazing for a lower temperature of 04. Traditionally terra cotta required the high bisque for majolica to avoid bleeding iron into the white glaze.

Marcia

Link to comment
Share on other sites

Thanks all I appreciate the feedback

 

I will do as Mark suggested and just get some new clay. I thought of bisque firing higher as Marcia said, but the way we work is to fire bisque and glaze in the same kiln at the same time, both at cone 05...limited time and budget, and we never have a kiln full.

 

Anyway, I have learned my lesson. I purchased the EM 215 without really knowing what it was other than it was an 05 clay with what seemed the right amount of color. I found out later it was a terra cotta.

 

Oh well, maybe I'll make some lawn...or here in New Mexico...dirt gnomes out of it

Link to comment
Share on other sites

  • 1 year later...

This thread got me thinking as I'm new to ceramics.  I started with AMACO #67 Sedona Red Clay and I'm doing slab building.  While I initialy had issues with joints that II atributed to the high shrinkag I finaly remedied that issue.  But I will be glazing this clay with a combination of brown and black glazes with a yellow underglaze.   Should i expect to see a lot of red poping through the glaze?   It was Bisque fired at 04. 

Link to comment
Share on other sites

Dark/red clays will darken the color of the glaze. How much depends on the color and opacity of the glaze, and if it's a breaking glaze or not (runs off of high points and settles in low points- good for showing texture).

in other words I should expect the color to come out darker than it would appear over a white or buff clay body, if the glaze color is lighter than the clay.  But with using dark colored glazes I should be in a better situation?.Do to the fack I want texture I could get it more with lighter colors. 

Link to comment
Share on other sites

Dennis, if you're going to continue using Amaco Sedona Red Clay then you should use their Artist Choice glazes. They look really great on that clay and show off textures very nicely. Google Amaco's website as they have great sample photos of what each color will look like. Also, while there check out the Opalescent glazes too.

 

Paul

Link to comment
Share on other sites

I think a missed issue here is, why was the supplier out of the clay she needed?  Living in a ceramic supply void for three years make me extremly grateful to Clay Works from Maryland for opening a store in Richmond.  The local studio I was using was always out of clay.  They had tons of storage space, but kept small amounts of stock.  Does clay go bad???  I have bags a year old, still good. I would buy several hundred pounds when available because I never knew when I would get more.  One good out come, I have tried out about ten different clays, using what was available in cone 6. 

 

 

Link to comment
Share on other sites

Dennis, if you're going to continue using Amaco Sedona Red Clay then you should use their Artist Choice glazes. They look really great on that clay and show off textures very nicely. Google Amaco's website as they have great sample photos of what each color will look like. Also, while there check out the Opalescent glazes too.

 

Paul

I'm waiting for a batch that are being fired right now.  I did use the Amaco Glazes only I used the F series.  Usine the Jet Black, Chocolate, and their Clear Transparent.  I looked tat the A series but noted that they only had 11 colors available while the F series had 31 color selections.   

 

Yes the opalescent glazes caught my eye as well.  The transparent pearl especially caught my eye and the thoughts were to try it as a final glaze coat over one of the F glazes.  

Link to comment
Share on other sites

  • 5 months later...

Well I got my first firing back from the opalescent glazes.  Wow do they create an interesting effect.  With the transparent pearl over a F series Choicolate Brown it produced an interesting color effect.  The brown was barely noticable and I would almost call the transparent pearl a white glaze.  

I just dropped off a another batch for glaze firing today.  I used a white and pastel colors in the F series as a base with the transparent pearl over it.  My hope is it will come out with just a touch of color pealing through the pearl.   I'm also trying the black tulip glaze on some other items with this firing.  I put the black Tulip over some Darker Blue and red base colors.  This i hope will create a similar effect with the items being basicly black with a bit of dark color peaking through.  Only time will tell.  

I have my first show on Sunday and it should be interesting.  This is not an art show but an aquarium show with most of pieces designed for aquarium usage. 

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...

Important Information

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