'Dead Glaze Bubbles' as an Advanced Age Sign
"Dead bubbles" can be used for verifying the age of antique Chinese ceramics. It concerns two different types or eras, general glazes(Ming dynasty and later) and the more ancient glazes, as explained for Jun glazes.
First we need to be aware that basically all glazes of Chinese ceramics contain bubbles. This can sometimes be used for age verification. Here we mention "dead" bubbles.
What are glaze bubbles?
These develop during the firing process in the kiln. Water contained in the glaze can form bubbles (steam) from which the water cannot escape. After cooling these remain trapped in the glaze. The size, distribution and uniform
After a very long time (usually hundreds of years) some bubbles close to the glaze surface may develop a tiny hole (not visible to the bare eye). Bubbles in contact with crackles inside the glaze can also develop these.
After more time some of these tiny holes change into straight tiny cracks (invisible without strong magnification). Still later these straight crack become cross-shaped ( a vertical and a horizontal crack). These minute openings can get infiltrated by dirt from the environment over time (not all do). This results in the bubble interior turning to a dark brown or black color. They are then called "dead bubbles" presumably because they are bubbles no more.
As it takes a very long time for bubbles to reach this stage, this can be a sign that the glaze is really old, usually several hundred years.
Please note however, that at present it is not quite possible yet to tell for sure from what era or period a glaze with dead bubbles is; it is only an indication that the item IS old or antique. (There is still further research needed. Each glaze type may be different.)