Kate Johnson on fri 15 oct 04
Hello, all--
I am somewhat nonplused at the moment, having gotten to see my kiln-load of
redware out of the bisque-firing last night. I've been trying to
approximate the effect of slip-decorated sgraffito of the 18th and 19th
centuries, and WHOA did something ever *not* go right!
Colors used in that period, on that type of ware, were often yellow, red
(terra cotta), white, dark brown, etc. (Also a brighter red and a green
color, but since I didn't want to use modern pigments and I also wanted to
avoid poisonous ingredients, I decided to stick with the first ones.)
SO. It was suggested I try yellow ochre for the yellow tone. I have some
Arroyo slip I've been using for the dark, and of course white earthenware
slip gives you white. This last batch was a real disappointment, though!
The yellow ochre mixed with white earthenware slip turned a light terra
cotta. The Arroyo slip, in some of the pieces a very dark brown, turned a
slightly darker--terra cotta. The clay body is terra cotta. Only the white
slip actually produced much of a contrast...
If you would, and have time, please go to my Yahoo pottery album at
http://pg.photos.yahoo.com/ph/graphicartepsi/album?.dir=4870 and take a
look--I've moved the unfired bird plate and the fired bird plate up to the
first row for your convenience. Normally, of course, I finish with a clear
glaze, but I brought this one home last night to photograph for
Show-and-Tell.
Suggestions, please!! I won't look good with all my hair pulled out!
Now mind you, I KNEW that yellow ochre, when heated, *will* turn reddish--I
used to do demos on primitive pigments and demonstrated that phenom to my
audience. So...shouldn't have been that surprised, but I'm left
asking--what DID our 18th c. forebears use to get the golden yellows (and of
course what's UP with my Arroyo slip?!?), and how do I do likewise while
keeping to colonial American methods. It wasn't glaze--it was slip.
Please help? I know that you can get colored slips, commercially pigmented,
and I suppose I can go that way if I have to, but this is bizarre. I'm
frustrated, AGAIN.
(By the way, the pie plate with the white earthenware slip decoration at
bottom is going to be gorgeous! So is Bird Plate 2, even though the raw
sienna color turned, you got it, terra cotta. The white is white, and the
Arroyo slip on IT made a brown so rich it's almost black. Go
figure...same/same as on the bird plate.)
Thank you, profusely, in advance!
Regards,
Kate Johnson
Graphics/Fine Arts
http://www.cathyjohnson.info/
http://www.epsi.net/graphic/
http://www.ebsqart.com/Artists/cmd_1494_profile.htm
Wood Jeanne on fri 15 oct 04
Hi Kate,
I am also trying to get the yellow of earlier pottery
with safe ingrediants ...only my attempts are for food
safe medieval pottery recreation.
This is what I have found: the yellow is always over
white(ish) clay. If it's on a red clay like terra
cotta it's because of a white slip over the red.
Lead glazes turn the white background yellowish and
the reason why seems to be that the lead glaze was
prepared over heat with iron instruments to stir and
they left a little iron rust which shows up over the
white.
I am currently trying stains in clear glaze base(s) to
get similar yellows. Not quite there yet, although the
colors are good they have been opaque or milky rather
than transparent yellow thus far.
Jeanne W.
--- Kate Johnson wrote:
snip:
I've
> been trying to
> approximate the effect of slip-decorated sgraffito
> of the 18th and 19th
> centuries, and WHOA did something ever *not* go
> right!
>
> Colors used in that period, on that type of ware,
> were often yellow, red
> (terra cotta), white, dark brown, etc. (Also a
> brighter red and a green
> color, but since I didn't want to use modern
> pigments and I also wanted to
> avoid poisonous ingredients, I decided to stick with
> the first ones.)
>
> SO. It was suggested I try yellow ochre for the
> yellow tone. I have some
> Arroyo slip I've been using for the dark, and of
> course white earthenware
> slip gives you white. This last batch was a real
> disappointment, though!
> The yellow ochre mixed with white earthenware slip
> turned a light terra
> cotta. The Arroyo slip, in some of the pieces a
> very dark brown, turned a
> slightly darker--terra cotta. The clay body is
> terra cotta. Only the white
> slip actually produced much of a contrast...
> Now mind you, I KNEW that yellow ochre, when heated,
> *will* turn reddish--I
> used to do demos on primitive pigments and
> demonstrated that phenom to my
> audience. So...shouldn't have been that surprised,
> but I'm left
> asking--what DID our 18th c. forebears use to get
> the golden yellows (and of
> course what's UP with my Arroyo slip?!?), and how do
> I do likewise while
> keeping to colonial American methods. It wasn't
> glaze--it was slip.
>
> Please help? I know that you can get colored slips,
> commercially pigmented,
> and I suppose I can go that way if I have to, but
> this is bizarre. I'm
> frustrated, AGAIN.
>
> (By the way, the pie plate with the white
> earthenware slip decoration at
> bottom is going to be gorgeous! So is Bird Plate 2,
> even though the raw
> sienna color turned, you got it, terra cotta. The
> white is white, and the
> Arroyo slip on IT made a brown so rich it's almost
> black. Go
> figure...same/same as on the bird plate.)
>
> Thank you, profusely, in advance!
>
> Regards,
> Kate Johnson
> Graphics/Fine Arts
> http://www.cathyjohnson.info/
> http://www.epsi.net/graphic/
> http://www.ebsqart.com/Artists/cmd_1494_profile.htm
>
__________________________________________________
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Kate Johnson on fri 15 oct 04
Hi Jeanne...
> Hi Kate,
> I am also trying to get the yellow of earlier pottery
> with safe ingrediants ...only my attempts are for food
> safe medieval pottery recreation.
It's that food safe thing that's a problem, isn't it! I've found a gorgeous
yellow 17th C. wine flask, but I satisified myself recreating the SHAPE, not
the color...
>
> This is what I have found: the yellow is always over
> white(ish) clay. If it's on a red clay like terra
> cotta it's because of a white slip over the red.
Hmmmm...will try that next. I thought it was just the heat on the ochre...
> Lead glazes turn the white background yellowish and
> the reason why seems to be that the lead glaze was
> prepared over heat with iron instruments to stir and
> they left a little iron rust which shows up over the
> white.
Interesting!
>
> I am currently trying stains in clear glaze base(s) to
> get similar yellows. Not quite there yet, although the
> colors are good they have been opaque or milky rather
> than transparent yellow thus far.
And of course I'm DYING for opaque! Good luck to you...the hoops we jump
through to recreate the past, eh??
Best--
Kate
Rudy Tucker on sun 17 oct 04
Kate,
A couple of years ago I was involved in the same quest of developing
slip/glaze colors of that time period without use of the more toxic
materials. I was especially interested in that warm transparent yellowish so
typical of lead glazed redware. To complicate my search I wanted to raw
glaze my ware as I do all my stoneware. At first I attempted to color the
slips with various oxides and stains. Slips were then covered with a clear
glaze as you are doing. I had some success with this approach.
As for the yellowish, better results came from coloring the glaze rather
than the slip. Jeanne Wood indicated that she is using this approach in her
reply. And she is at least partially correct on where the yellow tint comes
from.... iron. The earliest lead glazes were simply powdered raw galena
dusted over raw ware and fired. I've had no expirience using leaded glazes
but would think the lead would add little color if any. Jeanne is concerned
with midieval pottery and may be correct that the iron was contamination
from processing equipment especially the specks. Later lead glazes were
basically combinations of lead and clay. Most often, I would think, the same
clay used to form the ware. That then would be the primary source of iron
coloring the glaze. Because I'm single firing adding clay to the glaze mix
made sense for me. I had pretty good results using both local clay and Red
Art clay in glaze. You could try small additions of iron ox starting
with1/2%---or yellow ochre---or red art clay----or any local red clay. My
test were the same as Jeanne's, cloudy to opaque when using stains.
I might be able to send photos of tests if you are interested.
Good Luck,
Rudy
----- Original Message -----
From: "Kate Johnson"
To:
Sent: Friday, October 15, 2004 12:08 PM
Subject: Slip decoration pigments?!
> Hello, all--
>
> I am somewhat nonplused at the moment, having gotten to see my kiln-load
of
> redware out of the bisque-firing last night. I've been trying to
> approximate the effect of slip-decorated sgraffito of the 18th and 19th
> centuries, and WHOA did something ever *not* go right!
>
> Colors used in that period, on that type of ware, were often yellow, red
> (terra cotta), white, dark brown, etc. (Also a brighter red and a green
> color, but since I didn't want to use modern pigments and I also wanted to
> avoid poisonous ingredients, I decided to stick with the first ones.)
>
> SO. It was suggested I try yellow ochre for the yellow tone. I have some
> Arroyo slip I've been using for the dark, and of course white earthenware
> slip gives you white. This last batch was a real disappointment, though!
> The yellow ochre mixed with white earthenware slip turned a light terra
> cotta. The Arroyo slip, in some of the pieces a very dark brown, turned a
> slightly darker--terra cotta. The clay body is terra cotta. Only the
white
> slip actually produced much of a contrast...
>
> If you would, and have time, please go to my Yahoo pottery album at
> http://pg.photos.yahoo.com/ph/graphicartepsi/album?.dir=4870 and take a
> look--I've moved the unfired bird plate and the fired bird plate up to the
> first row for your convenience. Normally, of course, I finish with a
clear
> glaze, but I brought this one home last night to photograph for
> Show-and-Tell.
>
> Suggestions, please!! I won't look good with all my hair pulled out!
>
> Now mind you, I KNEW that yellow ochre, when heated, *will* turn
reddish--I
> used to do demos on primitive pigments and demonstrated that phenom to my
> audience. So...shouldn't have been that surprised, but I'm left
> asking--what DID our 18th c. forebears use to get the golden yellows (and
of
> course what's UP with my Arroyo slip?!?), and how do I do likewise while
> keeping to colonial American methods. It wasn't glaze--it was slip.
>
> Please help? I know that you can get colored slips, commercially
pigmented,
> and I suppose I can go that way if I have to, but this is bizarre. I'm
> frustrated, AGAIN.
>
> (By the way, the pie plate with the white earthenware slip decoration at
> bottom is going to be gorgeous! So is Bird Plate 2, even though the raw
> sienna color turned, you got it, terra cotta. The white is white, and the
> Arroyo slip on IT made a brown so rich it's almost black. Go
> figure...same/same as on the bird plate.)
>
> Thank you, profusely, in advance!
>
> Regards,
> Kate Johnson
> Graphics/Fine Arts
> http://www.cathyjohnson.info/
> http://www.epsi.net/graphic/
> http://www.ebsqart.com/Artists/cmd_1494_profile.htm
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
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melpots@pclink.com.
Kate Johnson on sun 17 oct 04
Hi Rudy--
Thanks for the helpful post!
> A couple of years ago I was involved in the same quest of developing
> slip/glaze colors of that time period without use of the more toxic
> materials. I was especially interested in that warm transparent yellowish
> so
> typical of lead glazed redware. To complicate my search I wanted to raw
> glaze my ware as I do all my stoneware.
Oh dear, I'm over my head already. What do you mean by "raw glaze"? Glaze
on greenware?
At first I attempted to color the
> slips with various oxides and stains. Slips were then covered with a clear
> glaze as you are doing. I had some success with this approach.
So far, I'm only getting good "color" with white and Arroyo slip, and not
always then. The various shades of yellow are all turning varying shades of
red-brown.
>
> As for the yellowish, better results came from coloring the glaze rather
> than the slip. Jeanne Wood indicated that she is using this approach in
> her
> reply.
Will have to try this next, it DOES make sense...though not wanting yellow
over some of the other colors, maybe...
Because I'm single firing adding clay to the glaze mix
> made sense for me. I had pretty good results using both local clay and Red
> Art clay in glaze. You could try small additions of iron ox starting
> with1/2%---or yellow ochre---or red art clay----or any local red clay. My
> test were the same as Jeanne's, cloudy to opaque when using stains.
Thank you, will test! When adding the yellow ochre to the slip, the first
batch just went away--didn't show at all. So I increased the amount of
ochre, and though it looked a nice yellow before firing, it turned red-brown
after. I'll try it as a secondary step in the transparent glaze...
>
> I might be able to send photos of tests if you are interested.
Very much so. That's very kind of you, thank you!
Best--
Kate
>
katetiler on mon 18 oct 04
Hi Kate!
I make traditional honey glazed slip decorated medieval style tiles,
and have also had my fair share of glaze disasters last year, when the
pottery supplier I use changed the format of the 'ready mix' honey
glaze without telling anyone - so I was forced into finding out what I
was really doing!
I now use either a leaded clear glaze, or an unleaded one and just add
red iron oxide powder - up to 5% strength if I want a really dark
honey that makes the background red clay look almost like a dark
treacle brown, or a 2.5% strength for a creamier yellow.
Unlike most of the USA potters, we in the UK have lots of choice of
pottery suppliers who supply ready mixed glazes, so we tend to be a
lot lazier about getting into the raw ingredients! The only thing I do
add is about 1% bentonite to the powdered glaze & iron mix before I
add any water, this helps keep the glaze in suspension rather than
sinking to the bottom & staying there. I don't tend to glaze fire more
than once every couple of months & it is a real pain to spend an hour
chipping glaze out of the bottom of the bucket!
I fire the work to about 1060 to 1090 degrees Centigrade, and I vary
the colour by the strength of the honey glaze and the temperature, so
that the results from my two electric kilns mimic the results I used
to get when originally firing tiles in woodfired kilns, with the
differences in heat round the kiln.
I use red terracotta earthenware clay that has 20% sand or grog added,
so that the tiles warp less and have more strength, and I use a
standard white decorating slip.
You can see the results at www.katetiler.co.uk
The difference for me in 'raw glazing' ie. placing the glaze onto the
unfired ware and firing both the biscuit and the glaze processes at
once is that this most closely copies the original way most ware was
fired in medieval times, they didn't have the wood or the time to fire
work twice, emptying the kiln inbetween & reloading. The results when
raw glazing using a lead glaze are that the surface of the ware is not
as shiny, the water vapour escaping through the surface of the ware
dulls the surface slightly and also creates a closer bond between the
ware and the glaze. This means that the resulting tiles are safer to
walk on as well as they are not as slippery!
The difference in leaded and unleaded clear glaze is again that the
unleaded glaze isn't as 'fat', and seems to give a thinner coating.
The lead glaze we use now is lead bisilicate, rather than galena,
which is lead oxide and very very toxic. Lead bisilicate is chemically
bound in a safer format that prevents leaching of the lead.
Lead is used as a flux, which lowers the melting point of the glaze
and helps it flow. The red iron content of the clay will tint a clear
glaze slightly yellow, but to see the full 'honey glaze' effect you
need to add more powdered iron oxide, or rust! In medieval times, most
potters would have placed a pot of small chippings of bits of lead in
to top of the kiln to oxidise into powder. They would have scavenged
bits of lead glazing from windows and drainpipes, maybe even bits of
lead pewter from spoons or plates. This would then become the galena.
If you want to find some written texts of these techniques, have a
look at the Dover Press reprinted copy of 'The Craftsman's Handbook'
by Cennino d'Andrea Cennini, originally published in the fifteenth
century, which is a series of recipes for artists materials &
techniques, including how to obtain white lead - but I don't recommend
following any of the recipes!
I hope this helps :)
Karen Elkins - aka Kate Tiler
katetiler on mon 18 oct 04
I forgot to add, the Ashmolean Museum in Oxford has a lovely website
called Potweb:
http://potweb.ashmol.ox.ac.uk/PotScope-cl-me.html
this is the index of the medieval pottery section.
Karen - Kate
Rudy Tucker on mon 18 oct 04
Hi Karen - aka Kate,
I enjoyed looking at your website and have a question about the floor tiles
in the commisions section. Were these fired in a wood kiln and is the color
difference due to the firing? Or is it due to differing amounts of iron in
the glaze as you indicate in the encaustic section? I am assuming you used
the same "base" glaze for all. Nice warm colors!
Lead bisilicate may be "safer" than using lead in any other form, I don't
know about. None the less, I hope you are being extremely careful not to
create dust when mixing and keeping it off your skin when glazing.
Good tiles to you,
Rudy
----- Original Message -----
>... You can see the results at www.katetiler.co.uk.....
> ...The difference in leaded and unleaded clear glaze is again that the
> unleaded glaze isn't as 'fat', and seems to give a thinner coating.
> The lead glaze we use now is lead bisilicate, rather than galena,
> which is lead oxide and very very toxic. Lead bisilicate is chemically
> bound in a safer format that prevents leaching of the lead.
Kate Johnson on mon 18 oct 04
Ooooh, I know! I passed that website along here a few weeks ago, it's
glorious! I'm in the process of trying to reproduce a 17th C. wine flask,
and I have the shape down if not the yellow-probably-lead glaze. Gorgeous!
>I forgot to add, the Ashmolean Museum in Oxford has a lovely website
> called Potweb:
>
> http://potweb.ashmol.ox.ac.uk/PotScope-cl-me.html
>
> this is the index of the medieval pottery section.
>
> Karen - Kate
Thank you for your long post on glazes, I'm putting it in my answers file
and will experiment further. Since most of the stuff I do is bakeware,
flasks, serving-ware, etc., must skip lead glazes, though...
Like you, I also do living history as a hobby and partially as a source of
income--I write and/or publish books of interest to living history
interpretors, and as an artist/potter also find myself _attempting_ to
reproduce things from my chosen period (mostly 18th C.) I've taught myself
to paint miniature portraits on bone or legal ivory, for instance, and now
exploring the more practical applications of redware.
Regards,
Kate Johnson
Graphics/Fine Arts
http://www.cathyjohnson.info/
http://www.epsi.net/graphic/
http://www.ebsqart.com/Artists/cmd_1494_profile.htm
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