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can i use a cone 6 glaze on a cone 9-10 claybody

updated thu 16 oct 08

 

Llewellyn Kouba on tue 14 oct 08


Clayart,

I have a client who has two high fired porcelain goblets. The client
would like to see a very dark gloss blue of some kind. I don't seem to
have any cone 9 really nice dark blues that are to his particular liking
? I have better blues in cone 6-8. If the use is to hold wine for a
liturgical celebration is the glaze vitrified enough?...in other words
if I use a cone 6-8 glaze is this glaze under normal conditions of
firing and maturation safe to use on a cone 9-10 clay body? Should I
have concerns about being food safe etc.? Thanks for your input here.


Llewellyn Kouba
Abbey Pottery

Josh Berkus on tue 14 oct 08


Llwellyn,

> I have a client who has two high fired porcelain goblets. The client
> would like to see a very dark gloss blue of some kind. I don't seem to
> have any cone 9 really nice dark blues that are to his particular liking
> ? I have better blues in cone 6-8. If the use is to hold wine for a
> liturgical celebration is the glaze vitrified enough?...in other words
> if I use a cone 6-8 glaze is this glaze under normal conditions of
> firing and maturation safe to use on a cone 9-10 clay body? Should I
> have concerns about being food safe etc.? Thanks for your input here.

Food safety is not a concern. Glaze fit is: a cone 6 glaze on a cone 10
body is liable to shiver, crack, or even flake off. This will be
immediately noticable after you fire them, but then you're back to
throwing new goblets. Might be ok, but might not -- if it looks good
after all, give the goblets at least 48 hours before giving them to a
client.

Blue is easy; I'd suggest just taking your most stable cone 10 clear gloss
and adding 2% cobalt carbonate to it and maybe 0.5% manganese oxide to
make it really dark. Of course, you need to test.

--
Josh Berkus
San Francisco

Tony Ferguson on tue 14 oct 08


The only way to know for sure is to test fire and do a water test and acid test.

Tony Ferguson

Llewellyn Kouba wrote: Clayart,

I have a client who has two high fired porcelain goblets. The client
would like to see a very dark gloss blue of some kind. I don't seem to
have any cone 9 really nice dark blues that are to his particular liking
? I have better blues in cone 6-8. If the use is to hold wine for a
liturgical celebration is the glaze vitrified enough?...in other words
if I use a cone 6-8 glaze is this glaze under normal conditions of
firing and maturation safe to use on a cone 9-10 clay body? Should I
have concerns about being food safe etc.? Thanks for your input here.


Llewellyn Kouba
Abbey Pottery



Take Care,



Tony Ferguson
Artist...Clay, Web, Photo, Video

...where the sky meets the lake...

http://www.tonyferguson.net

John Hesselberth on tue 14 oct 08


On Oct 14, 2008, at 11:58 AM, Llewellyn Kouba wrote:

> if I use a cone 6-8 glaze is this glaze under normal conditions of
> firing and maturation safe to use on a cone 9-10 clay body? Should I
> have concerns about being food safe etc.? Thanks for your input here.

Hi Llewellyn,

You will have to determine if it is vitrified enough yourself. In
most cases the answer would be 'probably not'. But if the clay body
has a water absorption of 2-3% or less at cone 6 then you could
probably use your cone 6 glaze on it without worrying. You will want
to check for glaze/body fit also though. You could see crazing or
shivering that you don't see on your normal cone 6 body. So, when
all is said and done, there is no quick answer to your question.

Regards,

John


John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

Josh Berkus on tue 14 oct 08


Llewellyn,

> Food safety is not a concern. Glaze fit is: a cone 6 glaze on a cone 10
> body is liable to shiver, crack, or even flake off. This will be
> immediately noticable after you fire them, but then you're back to
> throwing new goblets. Might be ok, but might not -- if it looks good
> after all, give the goblets at least 48 hours before giving them to a
> client.

The above advice assumed that you were going to fire the goblet, with
glaze, at Cone 6. If you fire a Cone 6 glaze to Cone 10, most of the time
it will run off the pot.


--
Josh Berkus
San Francisco

John Britt on tue 14 oct 08


Llewellyn ,

The question to ask is, what is the porcelain claybody and what is its
absorption at cone 6? Check the catalogue and it should list the numbers.

For example, if it is Helios from Highwater then the answer is yes. Helio=
s
has a less than 1% absorption at cone 6. You can use it successfully at
cone 6.

Let me know,

John Britt
www.johnbrittpottery.com/wks.htm
www.penlandpottery.com/
http://ncclayclub.blogspot.com/

Edouard Bastarache on wed 15 oct 08


Hello Llewellyn ,

check out this :

http://www.flickr.com/photos/potier/45653735/

The same glaze from C/04 to C/9


Gis la revido

Edouard Bastarache
Spertesperantisto

Sorel-Tracy
Quebec
Canada

http://www.flickr.com/photos/30058682@N00/
http://pagesperso-orange.fr/smart2000/livres.htm
http://www.flickr.com/photos/potier/20321056/
http://myblogsmesblogs.blogspot.com/
----- Original Message -----
From: "John Britt"
To:
Sent: Tuesday, October 14, 2008 8:59 PM
Subject: Re: Can I use a cone 6 glaze on a cone 9-10 claybody


Llewellyn ,

The question to ask is, what is the porcelain claybody and what is its
absorption at cone 6? Check the catalogue and it should list the numbers.

For example, if it is Helios from Highwater then the answer is yes. Helios
has a less than 1% absorption at cone 6. You can use it successfully at
cone 6.

Let me know,

John Britt
www.johnbrittpottery.com/wks.htm
www.penlandpottery.com/
http://ncclayclub.blogspot.com/



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