Achieving Blue Stripes With Cobalt Oxide

[britpot]

hi everyone, looking for some expert advice,

 

Hoping to add some blue stripes to white vases.

 

 

came up with the following options, which may or may not be right:

 

1. underglaze route

 

having cut the oxide 50/50 with frit 3124(?),dilute it with water and paint on the bisque

 

next add opaque white glaze (maiolica from mc6 glazes). the blue will hopefully show through on firing.

 

2. overglaze route

 

as above, but the oxide is painted over the white.

 

are these procedures sound?

 

s.

[Marcia Selsor]

Cobalt is a very strong colorant and tends to bleed like antique foo-blue dishes. I think the best thing to do is use a slip recipe that calls for about 5% cobalt which is a lot.

 

If you are using the ^6 majolica from MC6 an overglaze is best. Cobalt under the majolica will be a pale baby blue because the glaze is opaque. I would test the mix. 50/50 is too much cobalt.

[Mark C.]

I suggest underglaze for sharper lines less blurriness .

[Marcia Selsor]

Mark,

I would agree except the majolica is opaque and cobalt with the tin-glaze goes baby blue. I have used cobalt in that recipe from MC6G.

Marcia

[oldlady]

brit, i see this is your first post, welcome.  i have read your post several times and am still confused.  are you saying that you plan to mix the cobalt, the frit and the glaze in one container and apply it to the white vases which are a white clay that has been bisque fired?  or are you saying that you plan to mix cobalt half and half with a frit, apply that in stripes and cover all of it with a white glaze?  

 

your profile does not have any real information.  when someone posts for the first time, we never know if that person has just picked up a new "hobby" and thinks it is easy to just ask a question and the answer is simple or if the person is a long time potter who is trying a new technique.  could you sort of say where you fit in?

 

there is an easy way to do "blue stripes on a white glaze" and that is to use slip which is colored with cobalt for the stripes and cover the entire piece with a white glaze. 

 

this is a blue silp under a white glaze.  cobalt oxide is extremely strong.  this is cobalt carbonate and it is really strong.  test whatever you do so you do not ruin something you like.  cobalt oxide may cause very dark speckles.

 

my slip is simply clay slurry from throwing. ignore the other color slips, i am talking only about the background color.  i do not know why the picture printed twice.

[britpot]

hi, thanks for the advice.

 

I'll try making a 5% cobalt slip, taking the overglaze route to application.

 

I'm surprised majolica is THAT opaque, that it reduces cobalt to baby blue.

 

Have you tried any white glaze recipes that can let the underglaze bleed through, like in the original Delft ware?

 

personal info: I'm a yearling hobby-potter with whwel and kiln. The wheel is in a garden shed, and today in England it is 9 degrees, damp and foggy.

 

I'm trying to actually SELL something (cue laughter), and figured that tall, thin, stripey cylinder vases would work.

 

Thanks for the photos, Old Lady. That's the type of blue I'm after.

 

 

 

S.

[MatthewV]

Cobalt blue is a good selling color.

 

I usually paint it on my natural white stoneware and finish with a clear coat. The design work can be done on bisque ware with a pencil and eraser. My cobalt solutions are a gram of cobalt oxide, a little china clay, and water. A little bit goes a long way.

[Mark C.]

Marcia

I have less than zero knowledge with majolica

I was just thinking under a glaze for sharpness

[oldlady]

brit.

 

slip goes on raw clay, not bisque.  i am sorry that i may have misled you.  the new description of what you plan to do shows me that you need a great deal more help than i can give you.  what you describe probably will not work.  at all.  please look for more info before you proceed.

[Roberta12]

Brit, I do the same thing that MatthewV does.  Underglaze or colored slip on white bisque then clear over it.  You can draw your lines on your bisque with pencil or mark it off with floral or masking tape......or freehand.  Then apply whatever color you want, then clear over that.

 

Roberta

[Babs]

I put on on top of a majolica, is as sharp as your hand is steady!...

Usually cut the cobalt with a bit of frit, iron for a softer blue and stir between brush strokes.

[neilestrick]

Are the vases white glaze or clear glaze on white clay?

[britpot]

thanks for the informative responses.

 

great looking bowl, Babs.

 

so what goes into your mixing dish?

 

10 percent frit 3124, 10 percent iron, 80 percent cobalt oxide, then some water? something like that?

 

I'll be exploring both underglaze on raw white stoneware and overglaze on white majolica routes.

 

 

S.

[neilestrick]

Try Stroke 'N' Coat glazes. They work well both under or over glazes.

[preeta]

S what kind of lines are you interested in. 

 

for casual lines i've done what matthiew does. white glaze then cobalt lines and then clear glaze. actually since this is a vase form i would not even finish off with a clear.

 

for sharp lines ive done white porcelain slip with mason stain blue and clear over. never to be repeated again. i do not like tedious precise work. 

 

what i have also done (which i learnt here from Marcia from another thread) with both glaze and slip is white, then wax, scratch through the wax and fill in with the blue. 

[Babs]

ther ewas quite a lot of info on this in another thread.

I suggest glazing a tile with the glaze you are going to use, and make a number of tests with varying amounts of cobalt.

I use spoon fuls of equal cobalt oxide, frit which is in the glaze, iron and bentonite as a starter. and make a number of dilutions of cobalt from there
"Majolica Colorant Suggestions:
Gerstley borate is no longer being mined, and was erratic in quality when it was. It made color pastel through very
fine reticulation (break up) on the surface, and although I used GB when I began majolica, I now use frit as a flux
(with bentonite added) or commercial majolica decorating colors. Colorants with just frit settle quickly, have
limited brushability, and are very powdery dry. Some artists, like Matthias Ostermann, use this quality to work the
surface like pastels. My methods resist the motifs with wax before a solid ground color is laid in, and the addition
of bentonite or use of CMC gum to the frit + colorant mix aid brushing and hardens the dry surface. Bentonite
doesn’t mix easily w/water, so be SURE to mix dry bentonite, frit, and colorant first, then add water.
I use frit 3124. Others will work, with color reactions influenced by frit chemistry. To aid brushability, you may add
a small amount of glycerin (drug store item), or a few drops liquid CMC gum to the liquid mix.
For things that melt easily at low-fire temps (copper, cobalt, iron) try 1 part colorant, 1 frit, 1 bentonite by volume.
For more refractory ingredients, test 1 colorant, 2 frit, 1 bentonite.
1 part colorant, 1 frit, ½ - 1 bentonite 1 colorant, 2-3 frit, ½ - 1 bentonite
Copper (blue-green), cobalt (blue), manganese
(brown to plum w/3110), iron (brown)
Chrome (grass green), rutile (rusty orange), titanium
(ivory), most stains
Note that stains intended as “body†stains – to color clay bodies – are too refractory, even w/flux added, to make a
smooth surface on top of majolica glaze. Some of those stains: Mason 6020 Manganese-alumina pink, Mason 6485
Titanium yellow, one of the lavender Mason stains. I find that Vivid Blue is also rather refractory.
Some AMACO Velvet underglazes work for decorating on top of majolica base glaze: Mist Grey, Jet Black, Rose,
Maroon, Leaf Green and 350 Orange, Amethyst, Violet, Real Orange, Lt. Red, Red. Too refractory to use: Electric
Blue, Pearl Grey, Ivory, Hunter Green, Deep Yellow, Straw, Lt. & Med. Pink . Test others.
AMACO now makes a series of colors specifically for majolica decoration, the GDC series of products. Good range
of 36 colors. They work well right from the bottle for decoration on top of the base glaze. Prices for small jars are
$3.50-5.75, pints $12 -38.00. The colors will inter-mix, but as with the colorants they are made from, some are
strong colors, others weaker, so you may need to test amounts. E.g. 3-4 parts Yellow and ½ - 1 part turquoise
makes a nice chartreuse.
Linda Arbuckle Majolica and Lowfire Information http://lindaarbuckle.com
Page 2 of 10
Soluble colorants: cobalt sulfate (blue), copper sulfate (turquoise), manganese chloride (plummy brown), chrome
chloride (green). All are toxic raw. Do not inhale, ingest. They are also absorption hazards: do not handle these w/o
gloves. Soluble colorants are dissolved, rather than suspended in water, so they wick with the water making a very
uniform ground color and leave a soft edge,. If you want a white areas, or to retain motif colors, areas must be
waxed before applying soluble colorants. Over-wetting the glaze when applying solubles may move raw glaze and
cause color to migrate thru the pot wall and/or crawling. Too much water on the raw glaze may cause crawling in
the fired glaze." Marcia wrote this. but I think she was quoting Linda Arbuckle.

Do a search in these forums.

A member now passed, TJR has some photos in his gallery, have a look at them, subtle and strong blues.Crisp lines. Great potter