Advances in Visual Authentication of Age - Bubbles

[peterp]

                  Dead bubbles and crystallization and their use for dating.


1. The older a porcelain item is the more dead bubbles does its glaze develop.

2. With certain porcelain types when they reach a certain age the very top of the bubbles closest to the glaze surface get truncated to form a tiny hole; with increasing age this hole develops into a split that is first seen as a straight line, that again later develops into a cross (the initial hole is in the center).

3. With older ceramics as those dating from the Song dynasty, for example, these cave in to form round pits in the glaze. Over time dirt accumulates inside these.

4. With Yuan dynasty underglaze blue and underglaze red wares age does not show as collapsed bubbles; instead white spots looking like cotton flakes appear inside the glaze; these are the result of a crystallization process.*


Remarks:
- Not all ceramics develop dead bubbles.
- Dead bubbles can take a very long time to develop. The process may take many centuries.


* Crystallization within the glaze is another sign of considerable age. When the glaze is fired its mineral components become an amorphous mass; after a very long time it tends to return to its crystalline state.

[peterp]

To evaluate an item's authenticity usually we look at about 5 to 7 features or check points that must conform with the supposed age or time of manufacturing.

The content of a painted decoration can usually give a hint as to the time of manufacture, but with fakes these decorations may be copied.

With monochromes there is no other decoration (painted or other) present than the glaze.
It is therefore necessary to check the shape, bottom, glaze condition, weight, etc.
To check the glaze condition reliably and avoiding fakes it is necessary to magnify the glaze with a rate of 200x or more to see tiny details and ageing that could possibly be present inside (not visible with the bare eye). In addition, as of this time and faking situation, the glaze condition alone is seldom sufficient to decide on age (with very few exceptions).

Glaze age signs can be genuine, but they can also be faked. With monochromes this is often done by adding blemishes (damaging the glaze with various methods, or adding impurities, sand grains, etc.) to make it appear older. These methods include using acid, burying or scratching items and more. Often it is not possible to make sure.

The interior of vessels needs also be checked. Sometimes, while everything seems to be old otherwise, a look at the interior condition may debunk this right away.