Blues
GLAZE OF THE WEEK 13 THOSE MOODY BLUES
HPG HAS 12 BLUES TO USE
WHAT MAKES BLUE?
COMBINATIONS
Notice that at HPG sales when all the pots are displayed on tables, gleaming in the sun, the blue glazes shine and shoppers migrate to blue pieces. We all want to get a good blue in our reperatoires of glaze choices because it is beautiful. Here are some choices:
UH Blue is a very stable, mottled blue with carmel tan where it breaks thin, and requires a reduction firing to bring out the blue form of the iron interacting with the other glaze materials. The soft blue seems to float in the glossy glaze finish. Glaze of the Week #7 discusses UH Blue.
Blue Chun (Phil’s) has been retried and formulated so that a consistent satin royal blue is achieved in a cone 9 reduction kiln, especially nice on white clay or porcelain.
Purple Chun has also been retried with new formulation. It is tricky. Sometimes it shows some purple color, with a satin finish, but sometimes it is more blue than purple and has a beige color on the piece. It has been difficult to get a purple at HPG.
Chun Blue or Sky Blue is simply Chun with added cobalt carbonate, about 0.0125 to 0.05%%. It is very delicate especially nice on porcelain.
What makes blue in glaze is usually an added oxide or carbonate of cobalt to a good white glaze. Cobalt is the same mineral found in the blue gemstone called lapis lazuli which comes from the Congo.. It is a very expensive mineral so it is used sparingly. Adding more cobalt up to 2% will increase the intensity of the blue.
Royal Blue is a bright, glossy blue glaze, but it is not stable. This means that it has the tendency to run off the bottom of the pot and even ‘push’ other glazes down off the pot. Therefore it must be used only as an accent near the top of the pot with another more stable glaze like Chun or Nelson’s Transparent. An accent means a trail, brush strokes, or dipping only the lip of the vessel in that glaze after the first glaze is dry. Used with clear glazesit is bight royal blue. Used with Miller White it is a much lighter lavender blue.
Limestone Blue is a good blue which breaks into an opalescent white in certain areas where it tends to run. Though it has been very popular it is now discontinued because it contains barium which is not considered safe to use in a vessel for food or drink. The acids in foods could leach out the barium even in high fire glazes over time. However, there is still some around which should only be used as an accent on the outside of a pot. The amount of barium is very small, but safety in HPG glazes is important.
Long Beach Blue is interesting and very stable. On porcelain it is a light, semi-matte “Alice Blue Gown” blue with no color breaks unless very thin. On iron-rich clays it is a mottled blue where thick and green where it is thinner, very good on a carved piece.
1
Reitz Blue is made with the white base glaze formula by a potter named Don Reitz with added 2% cobalt carbonate. It is the same formula as Reitz Green except that cobalt is used for blue without added copper for Reitz Green. It is a rich royal blue with a satin finish and is very stable. It seems to stay blue where it is thinner, no breaks to black or brown on white clay. If a good, solid deep blue is desired, not too shiny, this is a good one for porcelain or dark clay. Hilde’s carved piece in the garden is a fine example. Midnight Blue uses the same Reitz base as Reitz Blue, but with 5% Cobalt Carbonate. It becomes a very dark shiny navy blue, good on all clay bodies.
Pete’s Cranberry has been a favorite glaze because iof its rich, shiny opalescent blue which sometimes has berry red edges. These features are especially pronounced when glazed with a dark clay body, but very weak, washed out blue or even beige on Porcelain if not well reduced. The iron has to be in the clay body perhaps with some other mineral. . Adding more iron to either the glaze or the pot does not enrich the colors. It is very rich on Death Valley and even more so on Jamaica or Black Mountain clays. Beware! It tends to run if on the outside of the pot, at least the current batch does. Keep it high and not too thick. Best to keep it on the inside of a bowl or if on the outside, make sure there is a good foot ledge to catch any drippings.
Rutile Blue provides a soft blue accent with other glazes when used as an accent. It is one of the iron glazes which has no cobalt, but which produces an irridescent blue due to the iron plus titanium in the mineral called “rutile”. The blue color is more likely to come out in reduction firings, plain white in oxidation firings with only a sugestion of blue flashings.
Stains/Washes: Cobalt blue oxide or carbonate thin slurry in water is used as an underglaze, “wash”, or overglaze. It can be used to create designs under or over a clear glaze. Not very much is needed to make a strong blue motif with a transparent glaze. Esther Nowell’s well known blue on white designs are a good example.
Blue ceramic stain is a powdered stain mixture of cobalt and other color enhancing minerals which is commercially available and costly. When mixed with clay body material such as porcelain it can stain the clay used for colored clay work such as marbeling. If a stain is mixed into porcelain or other white clay slurry or slip, it can be used as an underglaze to create a background color or design. The slip body must match the clay body of the piece or it will blister during firing. Different shades of blue are available such as Mazarin Blue or Delphinium Blue. Varying proportions of the stain produces light to dark royal blue which is very stable especially under a transparent glaze. Supin uses slips effectively.
Stoney Matte Blue is a soft pale blue/beige, useful for many applications.
Combinations with blue. G-Black has cobalt blue in the formula to enrich the black effect. When Nelson’s Transparent is placed over a piece which has been glazed with G-Black first, a bright royal blue comes out of the firing. This should be done as an accent for best effect. Trying to create a totally blue piece this way looks uneven.
On Miller White the cobalt blue glazes and stains appear as a soft lavender blue.
Attempts at HPG to make a purple or lavender glaze have failed to produce that color. Instead a more lavender blue seems to happen. Emily’s Purple is a satiny lavender.
Pat Harwood 10/12/06 ed January, 2009 ed April 23, 2009 Nov 2010
2