[cstovin]

Hi all,

Most of the pottery I fire I intend to horse hair or Raku; thus I bisque fire it to cone 06. Most ceramics, or other dishes that are used to eat off of, or bisque that you buy are typically fired to cone 04.

Say I accidentally fired some of my pottery that should have been fired at cone 04 at cone 06; and I had not intended on horse hairing these pieces, but rather using them for candy dishes, or ?? although they still could be sold as "decorative pieces", what is the real reason pieces are fired first at cone 04, then refired at cone 06?


I know I can put these few pieces back in the kiln and fire then at cone 04; then all is good - but I am left wondering really, what are the ramifications of:

1) having under fired my piece (fired at cone 06 instead of cone 04)

2) if it is a decorative piece, not intended for food, but still glazed with cone 06 for final product - does it matter that it was accidentally fired at cone 06 for the bisque firing?

Charlene

[SShirley]

I have bisqued to both 04 and 06. Some of my glazes pinholed at cone 06but not at 04. Of course the softer the bisque, the more glaze it soaks up, so with a thicker coating the glaze may look different. You might try a couple of pieces from your 06 firing just to see how finicky your glaze is. It really shouldn't matter too much.

Of course I am glaze firing to cone 6, so it sounds like you are firing earthenware, so that may be different.

[JessicaGrayCeramics]

cstovin, on 13 January 2013 - 06:20 AM, said:

Hi all,

Most of the pottery I fire I intend to horse hair or Raku; thus I bisque fire it to cone 06. Most ceramics, or other dishes that are used to eat off of, or bisque that you buy are typically fired to cone 04.

Say I accidentally fired some of my pottery that should have been fired at cone 04 at cone 06; and I had not intended on horse hairing these pieces, but rather using them for candy dishes, or ?? although they still could be sold as "decorative pieces", what is the real reason pieces are fired first at cone 04, then refired at cone 06?


I know I can put these few pieces back in the kiln and fire then at cone 04; then all is good - but I am left wondering really, what are the ramifications of:

1) having under fired my piece (fired at cone 06 instead of cone 04)

2) if it is a decorative piece, not intended for food, but still glazed with cone 06 for final product - does it matter that it was accidentally fired at cone 06 for the bisque firing?

Charlene

Charlene,
Bisque firing you work to 06 is perfectly fine whether it was meant for food use or not. The difference is Some clays become a little more solid at 04. Clays that are mid or high fire may need a slightly higher temperature to mature. However if you are using a clay meant for low fire I'm sure it would be absolutely fine that it is bisqued to 06. If you do wish to re-fire the piece to 04 before glazing the piece, just for piece of mind you can. However I do warn you that extra firings can put stresses on the wares and cause them to crack. I bisque fire to cone 04 on a regular basis with most of my work. If you take a look at the image attached you can see a lot of little protruding tabs that stick out on my work. I use a mid-fire clay and fire to cone 6 for the glaze firing. The way my work is made the tabs break off too easily at cone 06. So I have figured out that if I fire to cone 04 the strength of the tabs on my work is much greater. Bisque firing can also be done at cone 08. The cone necessary really depends on the clay body and the artists techniques. It is a personal thing depending on how you use your work. It is not necessary to bisque to 04 unless your work needs it for stability.

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[Lucille Oka]

This is not the definitive answer by any means it is just basic. There are many books and other potters that can explain this to you much better than I. I have not made a study of quartz inversion or what else goes on in the firing. But some manufacturers andsuppliers will give you detailed info about how to fire their clays. The book ‘Clay and Glazes for the Potter’ by Daniel Rhodes updated by Robin Hopper is a good reference for this question.

Cone 04 is often times the recommended bisque firing temperature of the clay supplier; they test their products and make this determination. It is a temperature that burns off the impurities, releases all of the gases that are emitted during firing and it also makes the clay sturdier to handle during the glazing.

If you do not do this burning off, your glazes can turn out dull, muddy or interfere in other ways with the glazes. But there are potters who do once firings. I cannot tell you their results. But when I do once firing some of the under glaze colors go fugitive. Some of the other colors are not as vibrant as when I do separate bisque firing.

Some clay suppliers recommend Cone 06 for bisque because the particular clay blends are sufficiently matured at that cone. But you must also pay attention to the recommended cone temperature and rate of heat rise to achieve it.

Deciding whether or not cone 06 or cone 04 bisque is the best it is up to you. If you are doing raku, which is usually nonfunctional ceramics, I can’t really see your dilemma, unless you don’t like your results. If that is the case make a change.

[TJR]

cstovin;
Beware the generalization. As in ;

"Most of the pottery I fire I intend to horse hair or Raku; thus I bisque fire it to cone 06. Most ceramics, or other dishes that are used to eat off of, or bisque that you buy are typically fired to cone 04."
Bisquing is an industrial technique developed by potters in Europe to reduce breakage from the many hands handling the work on the way to the kiln.
You cannot say that bisque is typically fired at 04. I bisque at 07. When my studio subletter wants to fire his sculptural cats in the same kiln, we fire the electric kiln at 06. This is expedient, so that we can get everything in. The purpose of the bisque is to harden the pot so that you can handle it, but keep it porouse enough to accept a glaze. Linda Arbuckle bisques at 05, because she wants a hard surface for her majolica. I typically fire stoneware and porcelain to cone 9 and 10. I prefer a lower temp. bisque because I pay for the electricity.The only generalization I could make, is that your bisque temperature is "generally", lower than your glaze temperature.
If you wanted to throw those pots back in the kiln to further harden them at 04, you could, but you would be using more electricity, and time.
I hope this helps.
TJR.

[OffCenter]

TJR, on 13 January 2013 - 09:45 AM, said:

cstovin;
Beware the generalization. As in ;

"Most of the pottery I fire I intend to horse hair or Raku; thus I bisque fire it to cone 06. Most ceramics, or other dishes that are used to eat off of, or bisque that you buy are typically fired to cone 04."
Bisquing is an industrial technique developed by potters in Europe to reduce breakage from the many hands handling the work on the way to the kiln.
You cannot say that bisque is typically fired at 04. I bisque at 07. When my studio subletter wants to fire his sculptural cats in the same kiln, we fire the electric kiln at 06. This is expedient, so that we can get everything in. The purpose of the bisque is to harden the pot so that you can handle it, but keep it porouse enough to accept a glaze. Linda Arbuckle bisques at 05, because she wants a hard surface for her majolica. I typically fire stoneware and porcelain to cone 9 and 10. I prefer a lower temp. bisque because I pay for the electricity.The only generalization I could make, is that your bisque temperature is "generally", lower than your glaze temperature.
If you wanted to throw those pots back in the kiln to further harden them at 04, you could, but you would be using more electricity, and time.
I hope this helps.
TJR.

Thanks, TJR. I would have said something very similar to that. Now, I don't have to. I bisque all over the place. Some clays I use need to be bisqued to around 02 because of all the impurities in them, some clays I only bisque to 020. Others 010.

Jim

[Chris Campbell]

I am posting a link to a previous discussion of bisque firing because there is some good information in it.

http://ceramicartsda...__fromsearch__1

Bisque firing is often misunderstood due to the necessity of a teaching facility needing to process everyone's work in a reasonable time period. They create rules to keep themselves sane ... Who needs to run a dozen different bisque firings to keep everyone happy/unhappy?

Bisque firing temps depend on what you want to do next once you get your own kiln.

[yedrow]

You can look at the bisqued pot as a vessel that can hold a volume of water. The lower the temperature of the firing the more water it can hold. You can look at the glaze slurry as a vessel too. In this case, the percentage amount of clay (and/or bentonite and some other chemicals) combined with flocculation/deflocculation, control the amount of water per unit of glaze. This is kind of represented by specific gravity (volume of slurry divided by the weight of an equal volume of water).

We have to have both volumes in balance if we want to have consistant control over the look of our glazes, if for instance, we want to sell a jar to someone who bought that same color last year. I haven't had the flocculation part down well so I have been bisquing at cone 010 to get more glaze on the pot per weight of water soaked into the bisque (remember the volume thing). However, thanks to John Britt's video!!!!! I'm not getting control over flocculation and I'll be bringing the temp of my bisquing up.

Bisquing serves a couple of purposes. It burns out the clay impurities that can bubble up through the glaze and leave jagged, partially exploded bubbles on the surface. In higher reduction firings unburned impurities weaken the body itself and worse, encourage the growth of cristobalite (that increases the likelihood of breakage during use) in poorly fired kilns.

Bisquing also strengthens the pot so that you can do stuff like dipping it into a slurry with thongs. This reduces loss during production processes. When I bisque to cone 010 I have to be careful with my work lest I puncture the sides with the dipping tongs. Most of the studios I've seen bisque between 04-06. That being said, clays are different, glazes are different, and processes are different. Each may require its own temp, and as you can see, there is a wide range of temps.

In your own studio it is likely that the hotter you bisque the less glaze you will get on your pot when you dip it. That often means that the finished pot will look weaker and have less color saturation.

Joel.

[Marcia Selsor]

One other reason for temperature choice of bisque is terra sig. When I have burnished pieces with terra sig, the sheen can go dull if it is fired above cone 09.
These would be pieces for saggar firing or horse hair or feathers.

For earthenware getting majolica, I bisque to ^02, higher than the final glaze at ^04. This gives the clay strength. It still takes the glaze, and it reduces the pin holing.

Marcia

[cstovin]

Thank you,

When I said that bisque is generally fired at cone 04, I was saying in the ceramics world; when you buy bisque from Duncan, Mayco, or ready to paint, it has typically been fired to cone 04. I haven't done much other than Raku or horse hair, and that I know most people have a preference of firing to cone 06;

Thank you all for the information - I just didn't know if because I had some dishes that were meant for possible food articles, if that meant that they needed to be re-fired at cone 04? I had called our local art center, and that was the suggestion - so I thought I would actually ask here first :0)
Thanks again - guess I better do more reading and research on this one, but am relieved to know that for what I do, it won't impact me much (for now)

C,

[Lucille Oka]

cstovin, on 13 January 2013 - 12:51 PM, said:

Thank you,

When I said that bisque is generally fired at cone 04, I was saying in the ceramics world; when you buy bisque from Duncan, Mayco, or ready to paint, it has typically been fired to cone 04. I haven't done much other than Raku or horse hair, and that I know most people have a preference of firing to cone 06;

Thank you all for the information - I just didn't know if because I had some dishes that were meant for possible food articles, if that meant that they needed to be re-fired at cone 04? I had called our local art center, and that was the suggestion - so I thought I would actually ask here first :0)
Thanks again - guess I better do more reading and research on this one, but am relieved to know that for what I do, it won't impact me much (for now)

C,

If you are concerned about purchased, bisqued ware then, it is what it is. You must make tests and adjustments for your own finishing techniques. If you want to make food service ware your glazes must be conducive that purpose. If you decide that you need a harder bisque make it so, but testing should be done first.

[Mark C.]

In my large gas car kiln I have not used a bisque cone in over 20 years. I bisque by color and pryro temps. After
I have two temp probes so I know what the temps are even if one fails.
In an electric I put in a 08 cone in sitter-99% of clay is porcelain to be fired to cone 10 in a glaze fire later.
I pay the bill as TRJ says so why burn more juice unless I have to.
Mark