First comment is on "popping out of the glaze". Both cobalt oxide in flow blue and manganese oxide in mulberry can rise to the surface and create a sintered effect. In the case of cobalt oxide, it is usually just the original oxide that surfaces, probably due to its concentration in the glaze phase exceeding its solubility therein. IN the case of mulberry, the manganese oxide can actually be reduced to metallic manganese, leaving a decidedly metallic surface on the glazed ceramic body, though the reason is again a supersaturated solution, the pigment "precipitating" to the surface instead of the bottom of the solution layer.
As for "ghost" images, the unassailable proof is found on those pieces that have a different "ghost" image on the reverse side than the image on the front of the piece. This proves twice, both that there were differently decorated items stacked together in the saggar, and that the ghost images communicated from the transferred decoration, not through the pottery but through the atmosphere above it to the adjacent pottery. That is a rather powerful concept once you grasp its full significance. The physical chemistry involved is comparable to quantum mechanics.
As for non-flown items having ghosts, as long as there was a glaze on a nearby piece that was receptive to the volatilized cobalt, ghosts can appear anywhere. (The actual chemical specie responsible for that "transmutation" (it is really "transportation", as nothing has been transmuted) is only speculated as far as I know, since there is no way to analyze a specific compound at kiln- firing temperatures.
As for "pearl" and "pearlware", they are two different animals, the first having derived from the second, but "pearl" is used as a tradename in this context, while pearlware refers - as you note - to dirty greenware that has been intentionally tinted blue, as "bluing" tints dingy cloth to "whiten" its appearance. When better, more pure raw materials used to make greenware became available, whiter greenware was the result, and less and less cobalt oxide was needed to make it LOOK white. Thus the arrival on the scene of "whiteware". At what point, precisely, does pearlware transition to whiteware? ROUGHLY, around 1840, though some very white greenwares were being produced in 1830, and some very dingy greenwares were still being made in 1850. Not every potter bought his raw materials from the same source. The "pooling" of the glaze is a reasonable measure, not in how much glaze pools, but in how much blue tint is evident in any place that the glaze is thick enough to sense its color.
By the way, I type with TWO fingers, and it isn't fast, but I can talk at just under the speed of light, so if you have a lot of questions, I'm at 757 427 3619, and I'm retired, so I have plenty of time if you want it.
Responses
« Back to index | View thread »