Cheryl Hoffman on thu 25 apr 02
Hi All...my head hanging in shame. I just made a major goof preparing a
glaze and can really use some help to fix it. I'm a relative newbie, only
have one clear glaze that works for me every time. In previous batches,
I've
used cobalt, RIO, & rutile for colorants. The glaze is called Clear Glossy
1214 W from Digital Fire Insight...it was given to me on a 3x5 card. One of
the other suggested colorant combos was for a Blue/green so I thought I'd
try
it. I mixed up a 10 pound dry wt. batch, came in to catch up on Clayart
email. Delete, read a few, delete, funky green color of copper,
delete....???...wait a minute...(light bulb comes on)...the copper I just
mixed...7 percent...was black...oh my God, I used oxide instead of
carbonate!
In a panic, I've gone through all my books to find the strength
ratio.
In Gill Bliss, "Practical Solutions for Potters" I found: copper oxide =
copper carbonate x 65
___________________
100
Most of the other books say that oxide is twice as strong as carbon
ate. So, can I just make up another 10 # batch and leave out the copper?
The colorants in the recipe are: zircopax 9%, tin 5%, copper 7%...the
recipe
didn't say oxide or carbonate, but I know that 7% oxide is way too much.
Can
I save the glaze? And yes, even using a lesser strength, I know it's not
food
safe.
Thanks, Cher H.
Paul Lewing on thu 25 apr 02
on 4/25/02 1:09 PM, Cheryl Hoffman at Redtop1647@AOL.COM wrote:
> So, can I just make up another 10 # batch and leave out the copper?
> The colorants in the recipe are: zircopax 9%, tin 5%, copper 7%...the
recipe
> didn't say oxide or carbonate, but I know that 7% oxide is way too much.
Can
> I save the glaze?
Sure! If you mixed another 10# batch with everything but the copper, and
mixed the two together, it would come out the same- but only if your copper
oxide were exactly twice as strong as your copper carbonate.
But that's a lot of glaze to risk on a test. I'd make up a small amount of
the no-copper version, maybe 1 pound, and do a line blend with the copper
oxide version. If you were to do a 10-step line blend, one of the points
would very likely be the same color as you're used to, and then you'd only
have to make up enough of the no-copper version to get it the same. Who
knows, you might like on of the other steps on the blend better, too.
Good luck,
Paul Lewing, Seattle
Cheryl Hoffman on thu 25 apr 02
Thanks, Paul. Good idea to do a line blend with another batch. I guess
it's
not the end of the world, is it? I suppose I'll make many mistakes that
turn
into discoveries as I learn. I'll be able to sleep now that I know I
haven't
wasted all those chemicals and time.
Thanks again, Cher H.
John Hesselberth on thu 25 apr 02
Hi Cher,
No use hanging your head about that--there isn't a potter alive who hasn't
made a similar mistake.
A couple comments. Yes you can salvage your batch by adding more clear.
Copper carbonate we get as potters, though, is usually not the copper
carbonate you find in a chemistry handbook. It is usually the mineral
malachite or a synthetic substitute. Therefore you have to be a little
careful calculating the ratios. The numbers I use are 5% "copper carbonate"
= 3.6% black copper oxide = 3.24% red copper oxide. That means the red
oxide number is right on what you found in the Gill Bliss book--the black is
a little different--0.72 to be exact. So you don't have to make a double
batch to equalize it--more like another 4 or 5 lbs.
And you are right, 7% is way too much to put in and have a good durable
glaze. But my real question is why are you mixing a glaze for the first
time in 10 lb. quantities? Most of us use 100-500 gram batches for a first
test. You may want to remix a 200 gram batch correctly, test that, and then
decide how/whether you want to salvage your bigger batch.
Regards,
John
on 4/25/02 5:09 PM, Cheryl Hoffman at Redtop1647@AOL.COM wrote:
> Hi All...my head hanging in shame. I just made a major goof preparing a
> glaze and can really use some help to fix it. I'm a relative newbie, only
> have one clear glaze that works for me every time. In previous batches,
I've
> used cobalt, RIO, & rutile for colorants. The glaze is called Clear
Glossy
> 1214 W from Digital Fire Insight...it was given to me on a 3x5 card. One
of
> the other suggested colorant combos was for a Blue/green so I thought I'd
try
> it. I mixed up a 10 pound dry wt. batch, came in to catch up on Clayart
> email. Delete, read a few, delete, funky green color of copper,
> delete....???...wait a minute...(light bulb comes on)...the copper I just
> mixed...7 percent...was black...oh my God, I used oxide instead of
carbonate!
>
> In a panic, I've gone through all my books to find the strength ratio.
> In Gill Bliss, "Practical Solutions for Potters" I found: copper oxide =
> copper carbonate x 65
> ___________________
> 100
> Most of the other books say that oxide is twice as strong as carbon
> ate. So, can I just make up another 10 # batch and leave out the copper?
> The colorants in the recipe are: zircopax 9%, tin 5%, copper 7%...the
recipe
> didn't say oxide or carbonate, but I know that 7% oxide is way too much.
Can
> I save the glaze? And yes, even using a lesser strength, I know it's not
food
> safe.
> Thanks, Cher H.
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Ababi on fri 26 apr 02
Your letter is not clear.
There is one thing I can tell you.
You try a new color: Mix a 100 gram batch.
Now this glaze you got can be used for handles, or as a majolica paint
over white it will give you green where thin and metal black where
thick.
Ababi
---------- Original Message ----------
>Hi All...my head hanging in shame. I just made a major goof preparing a
>glaze and can really use some help to fix it. I'm a relative newbie,
>only
>have one clear glaze that works for me every time. In previous
>batches, I've
>used cobalt, RIO, & rutile for colorants. The glaze is called Clear
>Glossy
>1214 W from Digital Fire Insight...it was given to me on a 3x5 card.
>One of
>the other suggested colorant combos was for a Blue/gree mix n so I
thought
>I'd try
>it. I mixed up a 10 pound dry wt. batch, came in to catch up on Clayart
>email. Delete, read a few, delete, funky green color of copper,
>delete....???...wait a minute...(light bulb comes on)...the copper I
>just
>mixed...7 percent...was black...oh my God, I used oxide instead of
>carbonate!
> In a panic, I've gone through all my books to find the strength
>ratio.
> In Gill Bliss, "Practical Solutions for Potters" I found: copper
>oxide =
>copper carbonate x 65
> ___________________
> 100
> Most of the other books say that oxide is twice as strong as
>carbon
>ate. So, can I just make up another 10 # batch and leave out the
>copper?
>The colorants in the recipe are: zircopax 9%, tin 5%, copper 7%...the
>recipe
>didn't say oxide or carbonate, but I know that 7% oxide is way too
>much. Can
>I save the glaze? And yes, even using a lesser strength, I know it's
>not food
>safe.
>Thanks, Cher H.
>________________________________________________________________________
>______
>Send postings to clayart@lsv.ceramics.org
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
| |
|
