William Jacob on fri 5 mar 04
Two questions for today.
1. How does lithium in a glaze reduce crazing. I assumed it was simply a
matter of substituting a glaze component with a lower COE for one with a
higher COE. (Li for Na) But according to my glaze calculating software,
the glaze with the Li2CO3 has a higher expansion but doesn't show any
signs of crazing. I'm working on a high alkaline base glaze (for the color
response) that doesn't craze. This seems to work so far, but I'm curious
to see if it will be crazed in a few months.
FF 3110 ------ 31
F-4 spar ----- 15
Wollast. ----- 6
ZnO ---------- 4
Silica ------- 24
EPK ---------- 18
Lithium carb - 2
2. The next question is just this. Does anyone care to test this one and
see what you think? I've reformulated Ron&John's wonderful "Raspberry"
glaze to increase the silica and alumina and decrease the COE. I'm all
out of tin so haven't tested it as raspberry, but with the colorants
from "Licorice" it's a great black. And it takes stains very well. Anyway,
it seems to be "student proof" and I'm hoping to use it as a base for
several color variants, but don't have any idea about its ability to hold
copper. Anyone care to lab test it?
FF 3134 ------- 13
Neph Sy ------- 17
Wollast. ------ 21
OM #4 --------- 23
Silica -------- 26
And how do I refer to this glaze. I took someone elses idea and altered
it, so I hate to not give the originator any credit. But calling
it "Raspberry Base Redo" just seems a bit odd, especially since it's not
always raspberry.
This is a great group, and always very helpful. Although you do argue
about the most asinine things, really. And go on entirely too long.
Thanks,
joe jacob
Ron Roy on sun 7 mar 04
Hi Joe,
It sure does - if it's replacing KNaO - if you just add it it will increase
the expansion of most glazes. Lithium oxide has a low expansion - but it
must replace another oxide that has a high expansion rate to lower the
expansion of a glaze.
Send me the recipe of the new and the old recipe - I'll check it out - and
what cone you are firing to.
If you just added Lithium carb - then you top up the silica and alumina -
then you get a lower expansion.
The redo of raspberry meets the criteria for a stable glazes except - the
SiO2 is almost at the limit of silica in our suggested limits for a stable
glaze. This means it may not be melted properly to provide durability - you
will have to get it tested to see what the copper release would be.
You are right - we do argue about the most asinine things some times - I
would like to know what you consider asinine however before I agree
completely.
How I handle renaming a glaze I have revised
R&J Raspberry - revised by RR (to lower expan) would be one way. The
obvious problem is - if you name it Raspberry then everyone will expect it
to be a chrome/tin red of some kind - and if it wasn't then you would be
misleading them and casting dispersions on the original.
I'm sure you will find a way to do what ever you think is right.
RR
> 1. How does lithium in a glaze reduce crazing. I assumed it was simply a
>matter of substituting a glaze component with a lower COE for one with a
>higher COE. (Li for Na) But according to my glaze calculating software,
>the glaze with the Li2CO3 has a higher expansion but doesn't show any
>signs of crazing. I'm working on a high alkaline base glaze (for the color
>response) that doesn't craze. This seems to work so far, but I'm curious
>to see if it will be crazed in a few months.
>
> FF 3110 ------ 31
> F-4 spar ----- 15
> Wollast. ----- 6
> ZnO ---------- 4
> Silica ------- 24
> EPK ---------- 18
> Lithium carb - 2
>
> 2. The next question is just this. Does anyone care to test this one and
>see what you think? I've reformulated Ron&John's wonderful "Raspberry"
>glaze to increase the silica and alumina and decrease the COE. I'm all
>out of tin so haven't tested it as raspberry, but with the colorants
>from "Licorice" it's a great black. And it takes stains very well. Anyway,
>it seems to be "student proof" and I'm hoping to use it as a base for
>several color variants, but don't have any idea about its ability to hold
>copper. Anyone care to lab test it?
>
> FF 3134 ------- 13
> Neph Sy ------- 17
> Wollast. ------ 21
> OM #4 --------- 23
> Silica -------- 26
>
>And how do I refer to this glaze. I took someone elses idea and altered
>it, so I hate to not give the originator any credit. But calling
>it "Raspberry Base Redo" just seems a bit odd, especially since it's not
>always raspberry.
>
> This is a great group, and always very helpful. Although you do argue
>about the most asinine things, really. And go on entirely too long.
> Thanks,
> joe jacob
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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