OXIDE WASHES & UNDER GLAZE
The pot pictured above was thrown by me and decorated by Canadian pottery Donn Zver, at a workshop over 30 years ago. It shows the decorating technique of using oxide washes on foam or sponge stamps as well as brushwork.
I apply the following oxide washes with brushes or with cut out sponge stamps. The stamps are made of firm upholstery sponge which can be cut to a specified design using an Exacto knife. Another method that some people use, is to form a piece of thick, yet bendable wire into a design your like, heat the metal to red heat and quickly press it into the foam, to the depth you want. It would be wise do this outside because of the potential of toxic fumes emitted from the burning foam.
Some of the oxides, like the red iron, have enough fluxing power and may not need any added flux. Some of the more refractory materials (Chrome oxide, for example), need some addition of a flux to give the best results. You can add a little bit of a frit like Ferro 3134 or a little bit of powdered, plain celadon glaze (about a teaspoon per cup as a starting point).
These are the washes I used in my C10 reduction firings. I haven't yet tested them on C6 in oxidation or in soda/salt firings.
Some of the recipes don't give specific amounts of water. Try for a watercolor consistency (slightly transparent when brushed on paper). When I test these washes, I do one brushstroke across the tile and then 1/3 the way in I start a second brush stroke and 2/3 of the way in, a third brushstroke. This will give you a good indication of what strength you want to use on your slips or glazes.
You might also want to strain these a few times through a fine mesh (100-200 mesh) screen to get a smoother application with brushwork.
*****PLEASE NOTE: Many oxide and carbonates are TOXIC!!!! Wear masks and gloves and use good studio practices when mixing and applying and firing pots with these colorants. It is always a good idea to have kilns either outside or in a separate, closed off room, with a good outside venting system.
Oxides like manganese, which is toxic, and dangerous when breathed in as a powder, is equally as dangerous when released as fumes during the firing.
#1 Powdered Illmenite 40 grams, Kaolin 13 grams, water 3/4 cup. This can give a strong orange color over temmoku and other glazes. You might way to try to test versions of both granular illmenite and powdered illmenite and another one with 1/2 and 1/2.
# 3 Blue 9 grams Raw ochre, 2 grams cobalt oxide, 1/2 cup water.
#5 Dark red/brown 10 grams Copper Carbonate, 1 gram red iron oxide, 1 tsp Grolleg or other China Clay, 1 tsp Colemanite, Gerstley Borate or Frit 3134 and enough water to make a watercolor consistency (should be just a tiny bit transparent when brushed on paper). You might want to try it thicker to see the difference.
#6 Blue Green - 1 1/4 tsp Cobalt Carbonate, 1/2 tsp Chrome oxide, 3 T. Albany slip (may try to substitute Alberta slip or try another test 1/2 Ball clay and 1/2 earthenware clay like Redart.)
#7 Blue - Red clay (Newman red, Redart,etc.)100 grams, Cobalt oxide 4 grams, Manganese Dioxide 4 grams and enough water to make it into a watercolor consistency. The iron in the red clay and the manganese soften the harsh blue that you can sometimes get using the Cobalt alone. This is a David Frith recipe, I believe.
#8 Nepheline Syenite 50 grams, Red Clay 50 grams. (I use Redart and sometimes make it like a thick slip and squeeze it out of a syringe to make little iron red dots on top of a stiff glaze.)
#9 Michael Cardew's recipe using American Spar and ball clay: Chrome oxide 20, OM#4 Ball Clay 10, Custer Feldspar 30, Silica 20, Fluorspar 20, 2 cups of water.
#10 Black nickel oxide 1 tsp, Red Iron oxide 2 tsp, one of two tsp clear celadon or Frit like 3134.
#12 Michael Cardew Aquamarine: 80 Chrome Oxide, 20 Cobalt Oxide, 20 Rutile and enough water to make a watercolor consistency.
#16 Colemanite or Gerstley Borate 30grams , Rutile 20 grams, Dry, Clear celadon 20 grams, 1/2 cup water.
#17 Blue to teal 1 tsp Cobalt carbonate, 1/4 tsp Chrome oxide, 1/4 cup water, 1/4 tsp of dry clear celadon glaze.
#18 Red orange: 1 T Red Iron Oxide, 1 T Rutile, 1 T. clear, dry celadon.
#19 Blue (Hatcher recipe) - 50 grams dry porcelain body, 30 grams Red Iron oxide, 20 grams Cobalt oxide.
#24 Black under glaze - 43 Black Iron oxide, 18 Manganese Dioxide, 15 Cobalt oxide, 15 Nickel oxide, 9 Chrome oxide.
#31 Replica Copper underglaze: Redart 20, Whiting 66, Copper oxide 14, 2T dry, clear celadon glaze.
#40 Rust Red: 2 T Red Iron Oxide, 1T cry, clear celadon glaze (a frit like 3134 might work well with this as well).
#41 Rust Gold: 5 tsp Red Iron oxide, 2 1/2 tsp Rutile, 1 1/2 T clear, dry celadon glaze.
#42 Green or Red: Copper Carbonate 2T, clear, dry celadon glaze 1T (frit like 3134 may work OK as well).
#43 Red (purplish) 10 grams copper carbonate, 1 gram cobalt carbonate, 1-2 tsp of Frit 3134 or clear, dry celadon glaze.
#44 Dark Brown (w/reddish tone) - 10 grams Copper carbonate, 1 gram Red Iron Oxide, 1-2 tsp of Frit 3134 or clear, dry celadon base.
#47 Yellow Green - 1/2 Copper Carbonate, 1/2 Rutile (by weight) + water to make watercolor consistency.
#50 Gold: Rutile 50, Frit P54 or equivalent. 50 by weight + water to make watercolor consistency.
#51 Red Orange: 50 Rutile, 50 Red Iron Oxide, 50 Frit P54 or equivalent + water to make watercolor consistency. (can go pretty red on high calcium white glaze)
#59 Green: Chrome oxide 1 T, Gerstley borate or Frit 3134 (boron frit) 1 1/2 tsp + water to make watercolor consistency.
#63 Pink or purplish brown: Manganese Dioxide 1tsp, 1/2 C water
#67 Red Underglaze: Red Clay 3 parts, Red Iron oxide 1 part + water to make a water color consistency. (for comparison, try versions using both weight and volume).
#71 Leach blue: Red Clay 10, Cobalt oxide 20, Red Iron oxide 30, Manganese Dioxide 40. + water to make a water color consistency.
#80 1/4 tsp Cobalt Carbonate, 3/4 tsp Frit 3124, 1/4 cup water. Light blue or lavender on a high magnesia glaze.
#83 Medium Green: 25 Cobalt Carbonate, 53 Rutile, 2 Chrome Oxide, 20 Gerstley Borate + water to make a water color consistency.
#86 Tan/Orange: 50 Rutile, 17 Titanium Dioxide, 33 Gerstley borate + water to make a water color consistency.
#87 Underglaze Blue: Cobalt oxide 30, Nickel Oxide 4, Manganese Dioxide 16, Grolleg 50 + water to make a water color consistency.
#89 Bright Blue: 70 Cobalt Carbonate, 20 Gerstley Borate, 10 Titanium Dioxide + water to make a water color consistency.
#91 Iron Yellow: 70 Red Iron Oxide, 30 Titanium Dioxide + water to make a watercolor consistency.
#105 Kawai Red (use under a limestone glaze) Black Copper Oxide 60, Zinc Oxide 28, Tin oxide 3, Hard ash (Rice Straw) 9. NOTE: Clean sweep available from cleaning maintenance suppliers is made from rice hull ash and may work as a suitable substitute.
Hope these can be a starting point for your own work.