Actually celadon glazes are no nore difficult to work with than most other glazes. The supposed "difficulty" is a marketing myth. (Works , doesen't it?
The color in celadon glazes comes from a small inclusion of iron oxide in the basically transparent or semi-transparent glaze batch. When fired in reduction conditions, the iron is reduced to the FeO state, changing it to a flux on the silica base of the glaze and this also causes the grey-green to bluish coloration of the fired celadon glaze.
Getting the "best" possible colors and surfaces out of ANY glaze is truly difficult.... but that is true of ALL glazes.....not just celadons.
The tendency to go from blue colors to green colors is based upon the chemistry of the base glass combined with the percentage of iron present. For example, small molecular equivalents of BaO present in the glaze melt combined ith about .5% iron ocide by weight will help to promote a bluish color, particlauiry in a Na2
O fluxed glass. Celadons can run from ice blue to almost a smoky green.
All that is necessary to produce celadon is between .25% and about 3.5% red iron oxide in the batch and then firing it in reducing conditions before the glaze surface becomes gas impermeable to the reducing agents CO (and or H). This iron can come as an addition of pure red iron oxide, or can come from an iron bearing clay material.
As to the "crackling"... this is actually a glaze "defect" called crazing. When you WANT it for visual effect...... you call this defect a "feature"
. It comes whern the frozen glaze (glass is actually a liquid... a supercooled liquid) has a coefficient of reversible thermal expansion (COE) that is greater than the underlying clay body.
On cooling in the kiln, the glaze then shrinks more than the clay body under it. Glass is strong in compression but quite weak in tension. The cracks are the glass fracturing to absorb the stresses of the tension created. Technically these cracks actually penetrate just slightly into the glaze/body interface layer.... and crazed wares are weaker than their non-crazed counterparts.
The museum curator's "yellow celadon" you sometime see labeled as a special category is just regular celadon glazes that have been fired in oxidation, not reduction. I am guessing that these pieces MAY have actually been "seconds" from the potter's point of view...... should have been celadon color
And no... they are not supposed to always have crazing in them. The best of them fit the underlying bodies perfectly. Take a look a the work of Shimada Fumio as a good example of this (and some stunning celadon on porcelain work).
Hope this helps.