[Clayart] High-calcium semi-matte 2 base over Newman Red engobe

[Paul Randall via Clayart]

Hi Ron,
Recently I came into possession of a bag of Newman Red engobe. I mixed up an engobe and have sprayed it onto a dark iron clay body (heavy with Redart) that I plan to glaze fire at cone 5 1/2. I tested my engobe and it works well. I would like to test this with a very thin coat of semi-matte clear. If I use High-calcium semi-matte 2 base, can you offer an opinion on what result I might expect? I would be decorating with Gosu slip brushwork (Black) and a white slip.
Thanks for a comment
Paul Randall


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[ronroy--- via Clayart]

Hi Paul,

Calcium does not work well with iron - at least that is my opinion
based on reading mostly. Zinc also is to be avoided with iron.

Magnesium works well with iron - just be aware - magnesium has a low
expansion rate which is best combined with KNaO to keep the expansion up

Of all our glazes wax wing has the most magnesium and you can see what
happens with iron in that glaze.

I would do some testing and make sure you do some slow cooling which
will give the most dramatic effect.

I'd like to see some pictures of your results.

If you would like me to make up a high magnesium glaze that is stiffer
I can do that but you would need to do some testing.

In my mind I still think like a potter but the flesh is weak.

RR

Quoting Paul Randall <pa...@plrandall.com>:

> Hi Ron,
> Recently I came into possession of a bag of Newman Red engobe. I
> mixed up an engobe and have sprayed it onto a dark iron clay body
> (heavy with Redart) that I plan to glaze fire at cone 5 1/2. I
> tested my engobe and it works well. I would like to test this with
> a very thin coat of semi-matte clear. If I use High-calcium
> semi-matte 2 base, can you offer an opinion on what result I might
> expect? I would be decorating with Gosu slip brushwork (Black) and a
> white slip.
> Thanks for a comment
> Paul Randall
>
>
> Get Outlook for iOS<https://aka.ms/o0ukef>
>

Ron Roy
ron...@ca.inter.net
Web page ronroy.net

[Paul Randall via Clayart]

Thanks Ron,
What you have told me is invaluable. We are learning the whole life, as a good friend once said to me.

I will mix Waxwing base and use the clay body to provide iron. I plan to fire up to cone 5 1/2 then down-fire slowly to 1700F then back up to 1900F, hold there for 15-30 minutes, then 50F/hr down to 1500F.

I read the note from your book regarding the potential for shivering and dunting when using the base without oxides. Do you think the high Redart clay body along with Newman engobe might provide sufficient iron to prevent this?

I will test as stated above and the let you know if a “stiffer” recipe is needed.

Thanks
Paul

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________________________________
From: ron...@ca.inter.net <ron...@ca.inter.net>
Sent: Tuesday, January 6, 2026 3:10:06 PM
To: Paul Randall <pa...@plrandall.com>
Cc: clayart <cla...@lists.clayartforum.com>
Subject: Re: High-calcium semi-matte 2 base over Newman Red engobe

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[ronroy--- via Clayart]

Hi Paul,

Tell me how much red art and newman you will use and I will calculate
it see if adjustments are needed.

Crystals grow at different temperatures so trying different slow cools
will give you good info. Be careful to not go over 1000C when
reheating - you don't want to remelt any crystals that have formed.

To test for delayed shivering (if contraction of glaze is to little)
put ware in the freezer for a day - that continues cooling and will
aggravate any problems.

If anyone is using our glazes and needs them reformed due to material
changes - let me know.

[Paul Randall via Clayart]

Ron,
The clay body I am using is Dark Iron Red made by Continental Clay. It is an earthenware clay (lots of redart) mixed with a buff stoneware. That body has 4.66% Iron and 1.21% titanium (empirical formula) given by Continental.

Over that clay body I sprayed a Newman Red engobe which has 4.93% iron (empirical formula.)

That combination is bisque fired and ready for glaze testing.

Over that clay body/engobe I plan to spray a very thin layer of Waxwing base glaze (no iron or Titanium added.) I am hoping for the base glaze to interact with the iron in the clay body in an interesting way.

I will fire to cone 5 1/2.

Thank you for information on adjustments to glaze base, if needed.

Paul

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________________________________
From: ron...@ca.inter.net <ron...@ca.inter.net>

Sent: Thursday, January 8, 2026 2:24:17 PM

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[ronroy--- via Clayart]

Hi Paul,

Just do the testing for shivering. A 10x's magnifier will help spot
any fractures - look at the rim and any ridges where stress will
accumulate.