Mayco Alabaster

[Potpotpotter]

Hello! I was wondering if anyone ever had any problems with Mayco Alabaster. I have noticed that whenever I have used it on my functional wear like mugs, they seep in the water test. I usually test my mugs by keeping a tissue underneath a cup filled with water. Rest of the mugs from the same batch, same clay, but different glaze were fine. But this one made the tissue moist underneath. Same happened with a small plate. I have attached a picture of that mug. 
the clay I used is Tuckers Speckled white Stoneware cone 6.

[Min]

Claybodies should be vitrified enough to not weep / leak even with no glaze on them when used for functional work and fired to mid or highfire.

Is this the clay you used? https://tuckers-pottery-supplies-inc.shoplightspeed.com/mid-smooth-stone-speck-clay-cone-6-stoneware-ecom.html

If that is the clay then in theory the clay should be vitrified enough to not leak with a posted absorption figure of 1.0 % but published figures can vary by +/- 1%. I would suggest running your own absorption tests. This is a good idea to to when using a new clay or every once in a while on an existing clay as materials can change.

How to on testing for absorption here if you need it, about 2/3 the way down the page, I would suggest doing the weight calculation test with several samples placed in different areas of the kiln. 

Edited January 7 by Min

[Kelly in AK]

That is strange, because it’s the clay body that’s usually the determining factor if a pot leaks. I say usually because it’s possible with a perfectly fitting glaze to have a porous body that doesn’t leak (for a while, anyway). Are you sure you’re getting to cone 6? Some bodies show a significant difference between c5 and c6. 

As @Min says, the sure way to rule out the clay is to test it for absorption. 

[Potpotpotter]

On 1/6/2024 at 7:54 PM, Min said:

Claybodies should be vitrified enough to not weep / leak even with no glaze on them when used for functional work and fired to mid or highfire.

Is this the clay you used? https://tuckers-pottery-supplies-inc.shoplightspeed.com/mid-smooth-stone-speck-clay-cone-6-stoneware-ecom.html

If that is the clay then in theory the clay should be vitrified enough to not leak with a posted absorption figure of 1.0 % but published figures can vary by +/- 1%. I would suggest running your own absorption tests. This is a good idea to to when using a new clay or every once in a while on an existing clay as materials can change.

How to on testing for absorption here if you need it, about 2/3 the way down the page, I would suggest doing the weight calculation test with several samples placed in different areas of the kiln. 

Thank you for your reply. Yes that’s the clay I am using. I will definitely run my own tests for this one.

[Potpotpotter]

On 1/6/2024 at 9:06 PM, Kelly in AK said:

That is strange, because it’s the clay body that’s usually the determining factor if a pot leaks. I say usually because it’s possible with a perfectly fitting glaze to have a porous body that doesn’t leak (for a while, anyway). Are you sure you’re getting to cone 6? Some bodies show a significant difference between c5 and c6. 

As @Min says, the sure way to rule out the clay is to test it for absorption. 

I used the cones and they bent as per the temperatures. But I am going to run few tests and also maybe aad a new program because I am also having issues with pinholes lately. Thank you!