Cutlery Marking At Cone 6 Ox

[Joseph Fireborn]

Does anyone have success firing a cone 6 oxidation glaze to matte smooth surface without cutlery marks? It seems practically impossible. I know it can't be, but I haven't had any success. I have came very close. I have some white mattes that barely scratch and instantly wipe away with your fingers, but still this isn't something I want to be selling. 

 

My most successful version of matte has been a combination of a matte glaze with a satin version thinly sprayed over the top of the matte surface, this turns the matte into a slightly more satin glaze which instantly stops the marking, but it isn't the surface I would prefer. I really want to have a beautiful white or black matte glaze that I can use for my personal dinnerware that I am going to be making soon.  I have old expensive commercial ware that was given to me when I got married and it marks even!

 

I am guessing that my best results are going to be settling for the satin combination and incorporating it into my design instead of just using it to rid myself of cutlery marks. 

 

Anyone?

 

 

[High Bridge Pottery]

My conclusion is it's pretty near impossible as the beautiful surface comes from devitrification so you will always be walking the fine line between rough and smooth surface.

 

You either have to compromise on it marking or compromise on the surface quality. Best I can do is the mark and easily rub off.

 

I think the only way to test is make some plates and use them. See how it holds up in use. I was pleasantly surprised how well my semi-matt glaze has held up the past year being used for strong coffee most days and having coffee left in for days. It actually looks no worse for wear even though it marks the marks come right back off.

 

Had some success with coloured clays to colour the glaze but I still wouldn't trust it not to leach the colours so only use on the outside right now.

 

Here is stoneware painted with terracotta with my matt white. Slightly rough texture, contains lots of clay and I still haven't worked out the best way to apply it, loves to jump on thick. Not cone6 but near enough. Also used the terracotta as joining slip, thought it could cause problems but nothing so far.

[oldlady]

joseph, having lived with many different china patterns over the many years since i got my first set, i have to say that NO matte glaze is good on plates.  besides the cutlery marks, the sound of a soup spoon on my Mikasa Arabella is awful.  i know i am not supposed to scrape the soup spoon but it does happen and is unpleasant.

 

why not try something not so difficult?  does everything have to be a challenge?

[Callie Beller Diesel]

Corningware cutlery marks. They sell a special cleaner, Barman's Friend, I think, that cleans it off.

I think as long as the glaze isn't scratching or etching over time, wipeable marks are probably acceptable.

[rayaldridge]

I lost interest in matte glazes for many many years, for reasons that had nothing to do with cutlery, but I don't think I'd want a matte glaze on a surface that food will come into contact with.  The sound of cutlery, as oldlady says, is unpleasant.  Also, it's my impression that matte glazes, especially ones which have not been tested, might be more vulnerable to leaching problems than a well-matured glossy glaze (probably not necessarily true of lower fire glazes.)

 

Here's a good chance for me to make the case that higher temps are better for functional potters.  Glazes matured at 8 or 9 or 10 are usually simpler and will tend to have fewer toxic ingredients than glazes at 6, or at least that has been my experience.  (I hasten to add that firing at 6 can produce wares just as safe, but I believe it to be more difficult.)

 

It may be useful to point out that if your cutlery marks can be wiped away, then what you are seeing is probably metal deposited in the texture of the glaze surface-- like metal on a sharpening stone.  Depending on the cutlery involved, this may not be wonderful.

[Joseph Fireborn]

why not try something not so difficult?  does everything have to be a challenge?

 

I don't know! I just like the look and feel of a matte glaze, so soft and so smooth. I think my plan is to use my black matte and spray a white satin over it to create a greyish area, it will probably give it more interest visually anyways. 

 

I don't know what it is about not accepting things. I have never been able to just accept that things are the way they are. I guess a part of me just never wants to quit trying to learn new things.

 

Eh, back to the drawing table. My wife is getting a little worried that we will never get some new dinnerware. 

[Joseph Fireborn]

Here's a good chance for me to make the case that higher temps are better for functional potters.  Glazes matured at 8 or 9 or 10 are usually simpler and will tend to have fewer toxic ingredients than glazes at 6, or at least that has been my experience.  (I hasten to add that firing at 6 can produce wares just as safe, but I believe it to be more difficult.)

 

I don't know much about the subject, but I have wondered about these advantages, can you explain them more? I understand that glazes at higher temps have less complicated mixtures because they don't have to have as many melting agents and the beautiful coloring usually comes from the reduction. However is this true for electric? What benefits does one have firing ^8 electric over ^6 electric? I have read a lot of articles about it, and I haven't seen many people saying that ^8 was significantly better than ^6. Some people say the colors are slightly better, but not enough to justify the cost of elements. I have only read this and never actually experienced this. I fired a few glazes to ^7 before and I didn't notice any differences at ^7 than ^6.

[neilestrick]

Here's a good chance for me to make the case that higher temps are better for functional potters.  Glazes matured at 8 or 9 or 10 are usually simpler and will tend to have fewer toxic ingredients than glazes at 6, or at least that has been my experience.  (I hasten to add that firing at 6 can produce wares just as safe, but I believe it to be more difficult.

 

I strongly disagree. The materials used in cone 6 glazes are no more toxic than those at cone 10. In fact, many of the cone 6 glazes I use have the exact same ingredients as cone 10 glazes, just in different proportions. Cone 6 glazes are no more complicated. I have many cone 6 glaze that are cone 10 glazes with as little as 3% Frit 3134 added to it. Take a look at a bunch of cone 6 glaze recipes and you'll see that the materials are mostly the same, with the exception of frits being used more at cone 6. But frits are no more toxic than anything else, and actually make glaze formulation simpler because they contain so many oxides.

 

As for a durable matte glaze: there are different ways to achieve matteness. One is by not melting the glaze enough. Any underfired glossy glaze will be matte. This is not a good way to make a matte glaze, because it is not fully matured. It will scratch very easily. The other way to achieve matteness is through crystal growth. Magnesium matte glazes are examples of this, and they can be quite durable. I've got a couple of magnesium mattes that are harder than some of my gloss glazes.

[neilestrick]

 

Here's a good chance for me to make the case that higher temps are better for functional potters.  Glazes matured at 8 or 9 or 10 are usually simpler and will tend to have fewer toxic ingredients than glazes at 6, or at least that has been my experience.  (I hasten to add that firing at 6 can produce wares just as safe, but I believe it to be more difficult.)

 

I don't know much about the subject, but I have wondered about these advantages, can you explain them more? I understand that glazes at higher temps have less complicated mixtures because they don't have to have as many melting agents and the beautiful coloring usually comes from the reduction. However is this true for electric? What benefits does one have firing ^8 electric over ^6 electric? I have read a lot of articles about it, and I haven't seen many people saying that ^8 was significantly better than ^6. Some people say the colors are slightly better, but not enough to justify the cost of elements. I have only read this and never actually experienced this. I fired a few glazes to ^7 before and I didn't notice any differences at ^7 than ^6.

 

 

I fired cone 8 for about a year before dropping down to cone 6. I found no benefit whatsoever to firing cone 8, however there were several problems. First, element life was about 30% less than at cone 6. Second, cone 6 clay is over fired at cone 8, and cone 10 clay is under fired at cone 8. So unless I wanted to mix my own, there was not an acceptable porcelain commercially available. Third, I found colors to be better at cone 6, since some things start to burn out at 8.

[Joseph Fireborn]

As for a durable matte glaze: there are different ways to achieve matteness. One is by not melting the glaze enough. Any underfired glossy glaze will be matte. This is not a good way to make a matte glaze, because it is not fully matured. It will scratch very easily. The other way to achieve matteness is through crystal growth. Magnesium matte glazes are examples of this, and they can be quite durable. I've got a couple of magnesium mattes that are harder than some of my gloss glazes.

 

I will look into this direction. Thanks for the information.

[Mark C.]

Another aspect is a satin matt-Thats a glaze that is in between matt and gloss

I fire to cone 10 and have a nice satin matt-its tough as snot.

These glazes are harder to come by as they cross the line and feel buttery smooth but look more matt.

I'm sure they exist at cone 6.

[High Bridge Pottery]

You both use terms durable and tough as snot, does this mean they don't cutlery mark or that they are just hard as nails?

 

I would like to talk about the scale of matte and if I could try and define a few categories. In my opinion a gloss glaze containing micro-crystals is not matte. I look at a tin white glaze, micro-crystals and it is still a gloss to me. This is what I feel you may be talking about Neil with magnesium matte.

 

I think there are the under fired matte, where it would go gloss if a bit hotter. Then you have a too high silica ratio matte that are soft, dusty and similar to how an under fired gloss would look but if you fired them hotter it would not melt to a gloss. Next are the high alumina ratio matte. These I find are not so dusty and the buttery surfaces that look so good. It is hard for me to explain in words but it is much more a fluid, if that is the right word, than a sintered dust. It's surface is almost burnished. Here I think are the hard as nails matte.

 

I am sure if I could keep over supplying alumina is would tend towards the sintered powder soft dust as with all the other oxides but I feel hidden in that border with the right mix may be the elusive glaze. Each oxide has some subtle oversupply characteristics before they all turn back into refractory(ish) things.

 

This test tile sums it up better than I could in 1000 words. High silica, bottom right. High alumina, top left. Under fired, top right. High flux(calcium) bottom left.

 

[Joseph Fireborn]

I have a few satin glazes that I use all the time that are very durable. Maybe I should try slow cooling them more and see if they will go more matte, and get that in between stage where it is just enough satin and just enough matte that it wont dinner mark and still has that soft feel.

 

I will also try slow cooling my current matte glaze and see if a few crystals make it tougher. Preferably like snot. 

[rayaldridge]

Well, I find the principle difference between midrange and high-fired porcelain to be beauty, at least in my eyes.  The only evidence I can offer is the two terrific John Britt books.  I have both and the Cone 10 glazes he shows are prettier, to my eye, than the equivalent Cone 6.  It's true that many of the handsomest of the Cone 10 glazes are reduced, but even comparing oxidation to oxidation, I find the high-fire glazes to be more beautiful.

 

It could also be that most of the pots I've made over my life were fired at 10 in reduction, which may have terminally influenced me toward the higher range.  I guess I conceived of firing at 8 to be a compromise between my love of the big fire, and practicality when working with an electric kiln.

 

The difference I found when working at 10 was that boron was not necessary to make a good bright glaze.  My glazes then were probably harder and more stable than the glazes I use now. 

 

I feel certain that Neil has the facts on his side, that midrange pots are by far the most sensible choice for potters with electric kilns.  I could probably be more sensible than I am, still I like the stuff I'm making now, so I guess I'll keep on.

[Mark C.]

My glaze fire yesterday was 13 hours up (kiln moves very slow near end of cones melting) and 36 hours to cool down-comes out after lunch on Monday

My satin matt likes even hotter Temps and slower cools-I tend to put them in my 12 cubic little kiln and fire to cone 11 for them

So does any glaze with crystal growth for me

[Marcia Selsor]

Calcium in a glaze as part of the RO2 flux will toughen the surface. maybe you'll have to tweak the recipe a little.

 

Marcia

[neilestrick]

You can control the degree of matteness in magnesium matte glazes through slow cooling. Slower cooling = more matte.

[Joseph Fireborn]

Well. I ordered my elements and I have a few more firings left. I will use them to experiment with some slow cooling for crystals. I haven't done that before. Thanks for tips and ideas.

[Tim T]

As Maria says, playing with the fluxes used in the glaze can have a significant effect on hardness. For example, Lithium tends to make the glaze softer, whereas from memory potassium will make it harder.

 

As an aside, I was thinking about using an old record player to test for cutlery marking - replace the arm with a knife and weight the tip, throw a disk with a hole, and leave it to play for 24 hours before looking at the result. My other half said I was going mad

[rayaldridge]

 

I fired cone 8 for about a year before dropping down to cone 6. I found no benefit whatsoever to firing cone 8, however there were several problems. First, element life was about 30% less than at cone 6. Second, cone 6 clay is over fired at cone 8, and cone 10 clay is under fired at cone 8. So unless I wanted to mix my own, there was not an acceptable porcelain commercially available. Third, I found colors to be better at cone 6, since some things start to burn out at 8.

 

 

Neil, Standard's 130 porcelain is rated for 7-9.  It is translucent at 8, but in fact, I've fired it to 11-12 in a wood burner and it held up surprisingly well.  It isn't terribly white, unfortunately, but no inexpensive porcelain is very white, in my experience.  It throws okay, about as well as most porcelains, and doesn't seem to develop a lot of flaws in drying, which has been a problem with other porcelains I've tried.

 

I had the opposite view of colors between 6 and 8, but that may be because of my background, which taught me to favor the softer colors of high fire.

 

I'm sure that you are correct about element life.  To me the added cost and time is worth it.

 

Although... I was interested to hear Tom Coleman say at a workshop a couple weeks back that he disagreed.  He said he couldn't tell any difference in element life, and of course he spent a lot of his career in an academic setting.  He also claimed to have studied the energy usage and said there was a lot less difference than many folks thought between midrange and highfire.  On the other hand, he was admittedly (though cheerfully) biased toward highfire and had little use for midrange work.

 

I suppose if I were a production potter who was for some reason limited to electric firing, I might gravitate toward midrange.  But these days I'm more of a hobbyist, and it's likely that I'll be gone from this world before I go through many element changes.  I'll still be able to fire a lot of pots before the first change comes up.

 

(I should add that I'm not under any illusion that the big fire makes better pots.  Some of the best pots ever made were earthenware-- I'm thinking of stuff like English slipware, Persian alkaline copper wares, MezoAmerican polychrome, and so on.  But you have to make what you like.)

[glazenerd]

Moh's Scale of Hardness

Calcium       1.75           Magnesium       1 - 2.5

Strontium    1.50            Zinc                   2.5

Lithium        0.60            Silica                 7.0

Sodium        0.50           Boron                9.5

Potassium   0.40

 

Nerd

Boron at 9.5 is what caught my interest in borosilicate glass/glaze.

[neilestrick]

 

 

I fired cone 8 for about a year before dropping down to cone 6. I found no benefit whatsoever to firing cone 8, however there were several problems. First, element life was about 30% less than at cone 6. Second, cone 6 clay is over fired at cone 8, and cone 10 clay is under fired at cone 8. So unless I wanted to mix my own, there was not an acceptable porcelain commercially available. Third, I found colors to be better at cone 6, since some things start to burn out at 8.

 

 

Neil, Standard's 130 porcelain is rated for 7-9.  It is translucent at 8, but in fact, I've fired it to 11-12 in a wood burner and it held up surprisingly well.  It isn't terribly white, unfortunately, but no inexpensive porcelain is very white, in my experience.  It throws okay, about as well as most porcelains, and doesn't seem to develop a lot of flaws in drying, which has been a problem with other porcelains I've tried.

 

Although... I was interested to hear Tom Coleman say at a workshop a couple weeks back that he disagreed.  He said he couldn't tell any difference in element life, and of course he spent a lot of his career in an academic setting.  He also claimed to have studied the energy usage and said there was a lot less difference than many folks thought between midrange and highfire.  On the other hand, he was admittedly (though cheerfully) biased toward highfire and had little use for midrange work.

 

 

I've tried the 130. Awful stuff, IMHO! Not at all like a good grolleg porcelain. I get your point, though, that there are options out there. I just didn't find an acceptable option from my supplier.

 

During the last 1/4 of a firing, the elements are on pretty much 100% of the time, so adding another couple of hours to get to cone 10 increases the energy usage a lot. That's not to say that it's going to add $50 to the cost of a firing, though. Firing cost, when broken down to cost per pot, is pretty low even when it's high. But as a percentage there's a big difference between cone 6 and cone 10. And when you sell cups for $100 like Tom Coleman it doesn't really matter how much the firing costs. If he didn't notice any difference in element life then he wasn't paying attention. Ask any kiln manufacturer and they'll tell you that firing hotter lessens element life.

[rayaldridge]

Neil, I think you're right about Tom and the elements.  It only stands to reason that higher temps eat up elements faster.

 

I don't know how I feel about your view of Standard's 130 porcelain.  As you say, it's not a grolleg body.  But I've been using it exclusively for over 25 years now, so I guess I've adapted to its awfulness.  When I was a production potter, I didn't feel I could afford a good grolleg.  Maybe I need to revisit that notion, now that I'm making fewer and higher-priced things.  But first I have a ton or so of 130 to use.

 

Ah well.

[neilestrick]

Neil, I think you're right about Tom and the elements.  It only stands to reason that higher temps eat up elements faster.

 

I don't know how I feel about your view of Standard's 130 porcelain.  As you say, it's not a grolleg body.  But I've been using it exclusively for over 25 years now, so I guess I've adapted to its awfulness.  When I was a production potter, I didn't feel I could afford a good grolleg.  Maybe I need to revisit that notion, now that I'm making fewer and higher-priced things.  But first I have a ton or so of 130 to use.

 

Ah well.

 

I'm not saying it's bad, it's just not for me. I like grolleg porcelain. If you like it, then stick with it. I wouldn't let price hold you back though. The way I see it, clay is cheap even when it's expensive. $1 worth of clay to make a $30 mug? That's cheap.

[rayaldridge]

True.  Though I have to say, back when I first started using 130, I was asking 6 bucks for a mug, and the clay wasn't a whole lot cheaper than it is now, unless I'm completely misremembering.

 

But the other day I sold a 60 dollar mug, so times change.