Vitrified Stoneware Strength: Cone 10 Vs.cone 6

[TBm]

GIVEN:

- Stoneware A has a broad firing range, Cone 6 - 10

- Stoneware B has a narrow firing range, Cone 5 - 6

 

I take that to mean the following:

- A vitrifies fully at cone 10

- B vitrifies fully at cone 6

 

 

QUESTION:

Is A at cone 10 more vitrified (and stronger) than B at cone 6?

Or are they basically equal in terms of vitrification and strength?

[Matt Katz]

GIVEN:

- Stoneware A has a broad firing range, Cone 6 - 10

- Stoneware B has a narrow firing range, Cone 5 - 6

 

I take that to mean the following:

- A vitrifies fully at cone 10

- B vitrifies fully at cone 6

 

 

QUESTION:

Is A at cone 10 more vitrified (and stronger) than B at cone 6?

Or are they basically equal in terms of vitrification and strength?

 

 

Good question,

That really depends on the clays themselves. Many Cone 6 clays are not fully vitrified anyway. So you want to ask for their absorption and density numbers. a full vitrified body will have a density of between 2.35 and 2.45 (g/cm^3) and an absorption of >0.5%, independent of temperature

[TBm]

 

Many Cone 6 clays are not fully vitrified anyway. So you want to ask for their absorption and density numbers.

- A full vitrified body will have a density of between 2.35 and 2.45 (g/cm^3)

- and an absorption of >0.5%, independent of temperature

Thanks, Matt. VERY helpful information.

 

More research needed. Excuse me while I once again disappear down the rabbit hole of seeking the right clay for my intended purpose(s).

[hansen]

I'll have to give deference to the moderator!! it is worth mentioning that for the most part even cone 10 stoneware is only partially vitrified and partially sintered. Sintering is likened to spot welding; stoneware never becomes completely glassy. Truly vitrified porcelain does become utterly glassy. So I guess my answer is that neither clay A nor clay B are truly vitrified, however, they might be "vitrified enough" as far as we are concerned. Back in the day cone 10 was looked upon as some kind of silver bullet that solved all problems, but historically many different firing ranges from cone 4 to cone 14 are workable stoneware targets, depending on the need. My guess is that one or the other of the stonewares mentioned has either talc or feldspar as flux with clays which without that flux would be underfired. The behavior of different fluxes at different temperatures leads exactly to the point the moderator suggests, which is, it depends on the clay body formula.

 

Strength of the fired clay is a separate issue, and there are a variety of tests for that, how to measure load under stress, tendency to chip or break when struck, and durability issues such as grinding with abrasives, etc.

h a n s e n

 

 

GIVEN:

- Stoneware A has a broad firing range, Cone 6 - 10

- Stoneware B has a narrow firing range, Cone 5 - 6

 

I take that to mean the following:

- A vitrifies fully at cone 10

- B vitrifies fully at cone 6

 

 

QUESTION:

Is A at cone 10 more vitrified (and stronger) than B at cone 6?

Or are they basically equal in terms of vitrification and strength?

 

 

 

 

[Matt Katz]

it is worth mentioning that for the most part even cone 10 stoneware is only partially vitrified and partially sintered. Sintering is likened to spot welding; stoneware never becomes completely glassy.

 

 

 

 

Not true,

A properly fired stoneware can become fully vitrified, and is in fact glassy. All clays at high temperature, assuming correct compositional ranges, go through glass and mullite formation at high temperature. Stonewares just don't look as glassy as Porcelains. But given their absorption and density values, they are in fact vitrified.That said, the temperature of maturation can be manipulated through alteration of the fluxes.

[hansen]

Matt: I agree totally with what you are saying however my criticism is that too often the standard available products in most markets yield an underfired end result. Furthermore, not all stoneware IS vitreous cone 10 stoneware. If the buyer wants vitreous, they need assurance that the product delivers it. Agree? Disagree? Thankfully, this still pertains to the original question!!!

h a n s e n

 

 

it is worth mentioning that for the most part even cone 10 stoneware is only partially vitrified and partially sintered. Sintering is likened to spot welding; stoneware never becomes completely glassy.

 

 

 

 

Not true,

A properly fired stoneware can become fully vitrified, and is in fact glassy. All clays at high temperature, assuming correct compositional ranges, go through glass and mullite formation at high temperature. Stonewares just don't look as glassy as Porcelains. But given their absorption and density values, they are in fact vitrified.That said, the temperature of maturation can be manipulated through alteration of the fluxes.

 

 

 

 

[Matt Katz]

Then you have to try Matt and Dave's Clays ( stoneware coming this summer)...end of commercial : )

 

Matt: I agree totally with what you are saying however my criticism is that too often the standard available products in most markets yield an underfired end result. Furthermore, not all stoneware IS vitreous cone 10 stoneware. If the buyer wants vitreous, they need assurance that the product delivers it. Agree? Disagree? Thankfully, this still pertains to the original question!!!

h a n s e n

 

 

it is worth mentioning that for the most part even cone 10 stoneware is only partially vitrified and partially sintered. Sintering is likened to spot welding; stoneware never becomes completely glassy.

 

 

 

 

Not true,

A properly fired stoneware can become fully vitrified, and is in fact glassy. All clays at high temperature, assuming correct compositional ranges, go through glass and mullite formation at high temperature. Stonewares just don't look as glassy as Porcelains. But given their absorption and density values, they are in fact vitrified.That said, the temperature of maturation can be manipulated through alteration of the fluxes.

 

 

 

 

 

[hansen]

Matt: Don't end the commercial. Clays are often formulated to be slightly underfired for the simple reason that the will thus resist warpage, especially when used as platters or plates. Explain how your product differs. Personally I like slightly over-fired work because i like what survives after a decade or more of heavy use and dishwasher exposure

 

h a n s e n

 

Then you have to try Matt and Dave's Clays ( stoneware coming this summer)...end of commercial : )

 

Matt: I agree totally with what you are saying however my criticism is that too often the standard available products in most markets yield an underfired end result. Furthermore, not all stoneware IS vitreous cone 10 stoneware. If the buyer wants vitreous, they need assurance that the product delivers it. Agree? Disagree? Thankfully, this still pertains to the original question!!!

h a n s e n

 

 

it is worth mentioning that for the most part even cone 10 stoneware is only partially vitrified and partially sintered. Sintering is likened to spot welding; stoneware never becomes completely glassy.

 

 

 

Not true,

A properly fired stoneware can become fully vitrified, and is in fact glassy. All clays at high temperature, assuming correct compositional ranges, go through glass and mullite formation at high temperature. Stonewares just don't look as glassy as Porcelains. But given their absorption and density values, they are in fact vitrified.That said, the temperature of maturation can be manipulated through alteration of the fluxes.

 

 

 

 

 

 

[Marcia Selsor]

GIVEN:

- Stoneware A has a broad firing range, Cone 6 - 10

- Stoneware B has a narrow firing range, Cone 5 - 6

 

I take that to mean the following:

- A vitrifies fully at cone 10

- B vitrifies fully at cone 6

 

 

QUESTION:

Is A at cone 10 more vitrified (and stronger) than B at cone 6?

Or are they basically equal in terms of vitrification and strength?

 

[Marcia Selsor]

True vitrification of a clay body does not have a range of 5 cones. A ^6 clay will be vitrified at ^6 and a ^10 clay will be vitrified at ^10. As previously mentioned, do an absorption test to see if the clay is absorbing water after fired to the stated vitrification.

Any clay that is fired to its vitrification point is strong and non-absorbent..including terra cotta and earthenware.