Can a high-fire cone 10 porcelain clay be fired to only cone 6 or cone 7 successfully?

[Annie Mackin]

Can I use a high-fire cone 10 porcelain clay and fire it at cone 6 or cone 7 - mid-range? Will it have matured enough to be strong and fairly non-porous? I am new to this. I am learning to make coloured porcelain clay beads. I mixed various colours of Mason Stains into my porcelain to create small coloured blocks to work with. My first full fire at cone 10 negated any colour that had red pigment in it! I have coloured most of my pug of porcelain and would like to be able to use it without losing the red pigment in the colours. Any suggestions? 

[Min]

Hi Annie and welcome to the forum.

I would run some absorption tests at midrange and see what the clay comes up at. Depends on what you mean by fairly non-porous. How to do an absorption test here if you need it, about 2/3 the way down. It won't be as mature at cone 6 as 10 but it might be strong enough for beads, again you would have to run your own tests. 

Which red stain did you use and what percentage? Is it stable at cone 6?

[Hyn Patty]

Also, you can purchase frits to add to high fire porcelains to lower the vitrification to a lower cone.  Fritts aren't cheap but you add only a little bit.

[Bill Kielb]

10 hours ago, Annie Mackin said:

Can I use a high-fire cone 10 porcelain clay and fire it at cone 6 or cone 7 - mid-range?

You can purchase midfire cone 5/6 porcelain, they are produced. Laguna frost was a favorite for us WC437 I believe, in the states.

[Annie Mackin]

Min, Hyn, and Bill, thank you for your responses and advice. Min, thank you for the link. It will be helpful in many areas as I learn more about ceramics. To answer your question, I used, for example, Mason Stain Deep Crimson at 10% (50g in 500g of wet high fire porcelain clay). It turned out a medium grey. It's a steep learning curve for me! I now see that the Mason Stain label says 1260°C maximum. I fired at cone 10, so I exceeded that temperature. True for all the other stains in my sample discs - fired at cone 10 , and any red pigment was lost. I am hoping to save my small blocks of coloured porcelain clay (they make up a pug of clay and hours of wedging!) that I make my beads out of. And that's why I wondered if I could use this same coloured high-fire porcelain clay and fire it at cone 6 or cone 7 instead of cone 10 and still end up with beads that are hard enough not to chip.

Hyn, you mention frit. This seems like an alternative to firing at a lower cone temperature. I looked on a few sites that sell frit and it seems it's mostly added to glazes. Can I add this to my porcelain clay body? Have you done this? If so, can you give me a little more guidance on using frit?

I think if lowering the cone temperature is practical, it would be the easiest solution to keeping my colours true?

[Min]

3 hours ago, Annie Mackin said:

To answer your question, I used, for example, Mason Stain Deep Crimson at 10

It’s the stain you used and not the firing temp that is why it fired gray. Lowering the firing to cone 6 won’t help. Mason Deep Crimson is a stain derived from chrome + tin. This type of stain requires a specific chemistry of the host glaze (or claybody although that won’t work) containing a high percentage of calcium (or strontium) with no zinc and preferably low alumina. Claybodies won’t meet the low alumina requirement and most likely won’t have sufficient calcium to develop the red colour. 
To get a red you’re better off using cadmium inclusion stain for claybodies If you look at the link below you can see the requirements that each stain has. For body stains look for ones that have a number one next to them in the reference guide. Some of the other stains that aren’t typically body stains will work as a body stain but do look at what the requirements for the stain in a glaze are and then extrapolate that to the clay body.

https://www.masoncolor.com/reference-guide

[Callie Beller Diesel]

+1 to everything Min said about the stains and chemistry.

If you want to see if you can work an inclusion stain into your not-so-red clay, there’s different techniques you can use to disperse the pigment that are less labour intensive than straight spiral wedging. The least physical version is to roll out the clay and dry it completely so you can slake it down and slurry mix it. This method has the benefit of being able to weigh your materials dry, so you can record an exact percentage of stain. It will be slow, however, due to the drying. 

If time is an issue, you can mix your stain with a little water to create a paste, and take your block of clay and cut it into slices. Layer the stain with the clay slices, and use the cut and slam method to wedge them. This will disperse the pigment evenly and quickly. A bit more sweat equity into this method than slurry mixing, but much less than spiralling it in. 

As far as durability at cone 6 for beads, it could be worth testing a few to see. The porosity is more of a concern for functional work, because you don’t want a vase or coffee cup to weep, and you generally want your clay and glaze to mature at the same point to avoid a lot of possible flaws. But if you’re not glazing and porosity isn’t a concern, clay that is fully mature at cone 10 could reasonably expected to be pretty sturdy at cone 6 or 7. 

[Annie Mackin]

Callie Beller Diesel, by an inclusion clay, do you mean add a red stain to the clay that I have already coloured, like Dark Red (has a #1 on the Mason Stain Reference Guide (Min, thanks)? I think that is what you mean. I have some Mason Stain Dark Red, so I will add this to my coloured clay that contains red pigment and see how the colours fire. I think I will fire at Cone 6 or Cone 7  and see what happens.

I really appreciate all the advise I've gotten here on the Forum. I am very grateful.

If I can come back to this post, I'll let you know how my colours turn out.

Edited May 30, 2022 by Annie Mackin

[oldlady]

annie,  read callie's post again.  she refers to an "inclusion STAIN" not an inclusion clay.  some stain manufacturers produce these stains.  i do have some but do not remember details.

[Bill Kielb]

2 hours ago, Annie Mackin said:

Callie Beller Diesel, by an inclusion clay, do you mean add a red stain to the clay that I have already coloured,

The reference to inclusion is also know as encapsulated. Generally where the colorant in the STAIN is encapsulated in zircon for stability. It’s just a way to make stain stable and insoluable in water and glass (as in glaze). The terms you may hear about the chemical combination of stains to make the colorant less soluble or more stabile are:

Zircon based stuff

• 1) lattice
• 2) inclusion (also often referred as encapsulated)

Other method you may hear on occasion

• Spinel stain

Just a chemistry way to make stains more stable and safe for use in ceramics. Maybe a thought, always check the color of your stains at various temperatures to know at what temperature they change significantly for you. In other words test, test, test …….

Edited May 30, 2022 by Bill Kielb

[Min]

@Annie Mackin, inclusion stains refer to stains that contain zirconium silicate with cadmium sulfoselenide. The cadmium referred to in an inclusion stain isn't actually encapsulated like it is sometimes referred to. It's actually the process of making the stain that is called encapsulation so the terms can get confused. What is important to understand is that inclusion stains, such as the Mason Dark Red 6021 can be broken down and release cadmium if the stain is subjected to harsh mechanical processes.

Cadmium is one of the most toxic substances in the potters arsenal of colorants and you do need to be aware of what you are using and to do so with appropriate care. Cadmium inclusion stains are far and away much safer to use than cadmium oxide (which for all intents and purposed is not used by studio potters because of toxicity reasons). It is really important to not use any form of mechanical grinding / mixing of glazes, slips or claybodies containing inclusion stains to avoid breaking the stain particles down and opening up the possibility of cadmium release. In other words don't use an immersion stick blender, blender, dough mixer etc to mix the inclusion stain into the clay.

Use the least amount you can to get the colour you are looking for, this could be more or less than the 10% you tried in your original red clay trial, you will have to test to see how much it takes.

[Bill Kielb]

Just to add Min makes a great point; however designated, inclusion or encapsulated the general meaning is the same. Mason for instance marks their encapsulated stains (basically reds and oranges made with cadmium) as such as well as their msds sheets. Just some chemistry, but no mechanical grinding is good advice for sure.

Edited May 30, 2022 by Bill Kielb

[Russ]

I use a Cerdec inclusion red that I use straight on a porcelain.  basically i wet my finger and rub the porcelain and the dab my finger into the cerdec and then rub onto the wet porcelain.  Then bisque fired and glazed with a clear and fired to c10. It remains really red.

You can see the cerdec red in the gums.  i do it this way because it would be almost impossible to do it after the piece is built and saves me a huge amount of frustration.

[Callie Beller Diesel]

Just a little extra info on stains that could be useful in the future.

First, it tells you on the Mason website if certain stains need specific chemistry to develop or not develop. They have a handy chart on that.

Also, Digitalfire has some good reading on what materials are, and why that’s important. Here’s a link to the article on encapsulated stains, but if you want some expanded reading, follow the blue links to more articles within the same website.

[ATauer]

I think you’ve learned some important things with ceramics in this thread- first, most importantly, always know everything you possibly can about your materials. Just like reading all the MSDS sheets and knowing everything you need to know about oxides you work with in glazes, with stains you always have to read the information easily available about them before you attempt to use them, as they are not completely benign, especially if you screw up and do something like ball mill them into a slip.

Secondly, with literally everything in ceramics, you ALWAYS fire a test tile before you do anything else. That is why everyone makes small 100 gram test versions of glazes and fires them, that is why you should absolutely be firing small test amounts of any decorative slip or if you make your own underglazes to see what the percentage of stain you are using looks like fired before you mix up the large amounts. And especially, especially , for colored clay you always always fire pretty small round test tiles to see what the colors will look like, usually using a standardized way of diluting the colorants with the porcelain so you can see gradations of colors , and you can see if there are any problems- but you also absolutely should have known that 1) Mason stains only fire up to 2300F, although some will go up higher. And within the very wide range that they can be fired they will fire at different colors/hues/saturation at different temperatures, so you need to always to a thorough series of test tiles at any temperature you want to fire at, and Mason provides so much important information that it is required you look at each color you are thinking of using, before you even buy it, to make sure you can use it in clay as a body stain or if you want to use it in a glaze that your glaze meets the right requirements. It is also extremely basic knowledge to know what inclusion/encapsulated stains are and how to work with them safely (especially since they are quite expensive!).  Before you probably wasted about 25 lb of colored clay, there is a ton of information available on the internet on how to work with colored clays, there area also books and blogs that explain  a ton about stains. There are several only classes you can take, YouTube videos, and Chris Campbell, while her course is too rich for my blood & I already probably know everything in her classes, has the first hour of her classes for free where you would have learned most of this really basic foundational knowledge, she also has blogs and written lesson that cover quite a bit of what someone often needs to know starting out (although her paperclay lesson is completely inaccurate and full of misinformation, don’t bother reading that one). 

I’m afraid in your eagerness you leaped over a bunch of things that you should have taken the time to find out about, instead of actually learning about how to work with stains in clays you simply just made 25 lb of colored clay that you will this time need to TEST before you do anything else, before you add an inclusion stain to ther red clays you mixed up, you need to take the plain porcelain that you use as well as a quarter to dollar sized coin test from every color you have and fire them all at cone 7 or 6, I would recommend cone 7 if possible to start with. With the plain test tile you need to do the absorption test but also, most importantly for how you intend to use these, you need to test how hard they are and how well they will stand up to regular life, one way you can do this that’s a little odd for the situation is the cutlery test, to see if a butter knife leaves marks on it. While this is usually used with glazes I think in this case it will help you know whether the beads will get scratched up after being carelessly tossed into a pile of other jewelry or packed in a small bag with a variety of potentially hard substances. If it scratches and does not seem to have a hard enough surface, I don’t think these will be usable fired lower. The colored test tiles are so that you know what the colors look like at that temperature, and if you do decide to go ahead with this and add an inclusion stain to your red bars, you will once again need to TEST by preparing test tiles with increments of the added inclusion stain and fire those so you can decide what looks best and you use that. 

As for frit, I use frit myself to make my cone 6 homemade porcelain completely vitrified, but it is not as easy as just adding frit to a regular clay body. You need to know how much feldspar is in the clay body, and usually you need to have around 28-30 feldspar in the clay to get it down to cone 6, which is more than the regular 20-25 feldspar that is in most porcelains. Then what you do normally is remove the amount of feldspar that you are going to substitute frit in for, once you know what the absorption is for the clay with the 28-30 feldspar, and guided by that you usually substitute in between 2-5% frit 3124 (do not use 3110 even if someone tells you to). It is really not as simple as taking a pugged claybody where you don’t know the recipe, and just dumping some amount of frit into it that you guessed. And because you will likely have quite a bit less feldspar, that means you would be adding in quite a bit of frit which gets very expensive. The only way I can see to do this is to test the absorptions of the clay at cone 6 and cone10, then do a line blend starting with 0 frit and adding 2-3 % every test bar, up to potentially 10% frit, and fire them all and test their absorptions. Hopefully you will get lucky and in the line blend will be an amount of frit that produces an absorption of >0.5%.  If not, you can keep adding frit, which will get really expensive, or you could try adding some feldspar, again in a line blend, see how low you can get the absorption just with the feldspar, and then at that point do a line blend for adding frit which is hopefully less. Using frit to make a claybody vitrified- the people who talk about it are not at all talking about taking premade up claybodies and doing that, they are talking about how to do it for home made recipes or suppliers who are trying to make a cone 6 version of a popular cone 10 body, they do not mean for you to add it to clay you buy. It’s really complicated as you see, especially since it is extremely rare to know what the recipe of your bought clay is, which you need to do this process. Having just taking CMW’s clay class and learning about it and doing it myself with my own porcelain to get if to vitrifiy at cone 6 instead of 10, it takes a ton of testing and ideally also density tests. I’m lucky in that my cone6 porcelain has a great vitrification curve so it appears I could still use it at cone 10 if I wanted, but  most porcelains are not like that. It would also like make a mess of the colored clays she has already made, say she discovers how much feldspar and frit to add to her porcelain to make it, if not vitrified, at least hard and strong enough at cone 6, she has to determine how much dry weight feldspar and frit to wedge into her color blocks, and likely it would change the color of her blocks and she’s have to do test tiles of them all over again to see how they’ve changed and potentially add more stain to them. 

I wish you luck, try looking before you leap in the future, there are resources and classes and free youtube videos and lessons, and while it can be hard to find these days, there is an extremely excellent book called Colouring Clay by Jo Connell, it is hugely expensive to try and buy used and I had to do inter-library loan to read it, as my own extensive library system for a major city didn’t have it, but you usually can get it through your library and it is very much worth it to learn a ton of information, and especially learn all the beginning things you need to know to get started. I have a list of classes that I am going to be putting up online, Intro to Paperclay if for sure first, and then from a number of people pleading I think I had to bump tile making and mold making higher up on the list, .but this is making me wonder if I shouldn’t put using colored clay as second, while I said there were resources, and god knows I somehow learned it all but a lot of that was self taught and having read so much about everything else that I knew a ton about stains from glaze chemistry, honestly I’m not sure where I picked all the rest of it up. But there are basically two classes online that you can find and they are by well known color clay artists, although one has far more credentials for his artistry than the other one, but they are both quite expensive. I plan on producing really good quality classes but not charge an arm and a leg for them, and have discounts for certain members of society. I plan in making up for not charging as much for them by hopefully getting a lot more students, and also instead of just doing the one class they do offer lots of classes on quite a variety of topics, as a sculptor I have really deep knowledge of a lot of different things that come together in my work, plus I also sculpt in glass so I have additional topics for classes, so far I’ve come up with over 15 classes that I can offer and that isn’t even counting doing some advanced versions of some of them. So I can charge less per class because I will have so many classes that it should even out. So I guess be on the lookout in the next year, for an online class covering colored clay.