How to add speckles to a claybody?

[GEP]

I am trying to decide whether to switch claybodies, to one from a manufacturer that isn’t having supply issues right now. The new one is the right color, and otherwise performs the same as the current one. The only thing missing are the speckles. Is it possible to add speckles to a non-speckled claybody? I actually use two different clays, and pug them together in a pugmill, so adding another ingredient to the pugging would not be hard. I’m looking for guidance on materials to try, and how much. I want it to look like the following photo:

 

[glazenerd]

Granular Magnetite (iron) at 2%.  From wet clay calculate 20% as water. 10lbs minus 20% water(2lbs) = 8lbs. Dry x 2% granular Magnetite. Judging from pic- 20 mesh speckles.  Make a 500 gram test batch and fire as a tile with usual glaze to judge speckle population. Add or subtract as per personal preference. Iron will be safer in your case given kiln location: granular manganese can fume. 

[neilestrick]

The speckles in the clay body I use at my studio is from granular manganese. I'd run a test with both the manganese and magnetite and see if there's a difference in how it looks in your clay body. Plus your old supplier can probably tell you which they used. With a well vented kiln I wouldn't worry about the fuming.

[Min]

@GEP, the Saftey Data  Sheet for the speckled clay body you like should indicate if there is manganese in the body. 

[Chilly]

Old Forge Creations has a post on this:

https://www.instagram.com/p/CWwKv9yLq5F/?fbclid=IwAR3SXVC8DqyCmsrfAcsCKPB87bvhJOQIMqMfLVVYh8Dsxwn_n9PIPIL7VRk

 

 

Edited November 27, 2021 by Chilly

[GEP]

Thanks everybody! I went looking for more information about my current clay, and there it was right in the description “granular manganese.” I also found some good tips about adding it to clay on DigitalFire. Time to buy some and do some tests. 

Sometimes the speckles in my current clay are unreasonably huge. I’ve even put some pots in the seconds pile because of weirdly large speckle splotches. So it might be nice improvement to have some control over the particle size now. 

[JohnnyK]

Have you thought of splattering the black spots onto your last glaze layer with a stiff toothbrush? With some practice you could come pretty close to your example and you wouldn't have to add anything to your clay...

[GEP]

44 minutes ago, JohnnyK said:

Have you thought of splattering the black spots onto your last glaze layer with a stiff toothbrush? With some practice you could come pretty close to your example and you wouldn't have to add anything to your clay...

Yup, I’m considering this possibility too. I’m taking a couple of months off after the holidays, and will spend this time testing several options. Or, if my current clay supplier recovers from its current issues, I may end up sticking with the current clay. Just need to have a plan in case they don’t. 

[GEP]

I think I’ve figured out what I’m going to do. I used 60-80 mesh granulated manganese, in the percentages shown below. Interesting that the speckles are sometimes larger depending on the glaze, because the glaze can cause them to spread out a bit. The 0.2% test looks the closest to my previous claybody. But there have been times in the past when I wished they were a bit more sparse. 0.1% is too sparse though, so I think the right answer for me is 0.15%.

 

[Mark_H]

Oooh, I like that second in from right.   Reminds me of enameled steel camp plates/pots.

 

[Harold Roberts]

Jumping back a bit to glazenerd's suggestion, granular magnetite, since it is a form of iron does it's color reflect a warmer iron color than granular manganese which is a blackened brown. I have used granular Illmenite but it produces very fine but very warm iron specks.

[smith]

Noob here.  Is this with oxidation firing?  If so, where do I buy manganese?

 

Edited January 9, 2022 by smith

[GEP]

1 hour ago, smith said:

Noob here.  Is this with oxidation firing?  If so, where do I buy manganese?

 

Yes, I am firing in oxidation. Check first with your local supplier. Mine did not carry granular manganese, but I found several places that sell it online. I ended up buying it from Brackers.

https://shop.brackers.com/granular-manganese-60-80-mesh/

[smith]

Thank you,  I like the store info too.

[Localpotdealer1234]

Do you have to fire in oxidation to achieve that desired look ? 
 

also a noob I really want to attempt making my own speckled clay but don't know much about oxidation firing. 

[Harold Roberts]

I am firing at cone 6 in an electric kiln. I make my own clay for many reasons. Most of the clay bodies available have way to much manganese and therefore very dark. Manganese makes a very cold dark brown and is poisonous. I was looking for a warm rich orange brown look. For that I chose iron magnetite. Also I found that the commercial blends do not have good glaze fit for my glazes. I also raw glaze (no bisque) and need a very tight body without any coarse materials in it like grog or fireclay that would absorb excess water to rapidly. I say this to warn you about why my claybody is formulated the way it is but it is a good starting point and one can add grog or substitute fireclay for the #6 tile.

Cone 6 stoneware

#6 Tile ..................24 lbs

Ball clay .............. 24 lbs

Goldart clay ..... 20 lbs

Redart clay ,,,,,,,,, 8 lbs

Flint ,,,,,,,,,,,,,,,,,,,, 12 lbs

Feldspar ............ 12 lbs

Iron magnetite ...120 grams

[Min]

@Harold Roberts, thanks for sharing your recipe, looks like a nice claybody.

Yes definitely, care must be taken when firing manganese to use a very well vented kiln, (whether in a glaze, slip or claybody) as the fumes from manganese are toxic. As to the colour difference I suppose that's a question of personal preference.

@Localpotdealer1234, if you fire in an electric kiln it will be firing in oxidation or a neutral atmosphere. If firing in reduction then yes you can get iron speckling (depending on the claybody).

Image below taken from Digitalfire, same claybody with the same glaze fired to the same cone. Test piece on the left oxidation fired and reduction fired on the right.