The following is from Bob Stevens, The Collectors Book of Snuff Bottles". Chapter 5, Glass Bottles I want to share it here because next to the inside painted, and stone type bottles, this type of snuff bottle is another personal favorite of mine, and look forward in time to adding some nice examples to my collection.
Overlay Glass Bottles The technique of making overaly glass bottles involves superimposing one of more layers of glass of different colors over the basic blown or molded glass bottle. Repeated dipping resulted in a cased glass made up of different colors in the successive layers. Then the outer coatings or casings of glass ere cut and ground in a design executed in cameo style, until the innermost layer of glass became visible. The resulting design in relief was engraved and polished, and the innermost layer was smoothed and polished.
While five layer overlay bottles have been rumored to exist, as far as I (Bob Stevens) know they are still an unverfied imagining. A few bottles with four distinctive layers still rank as those showing the highest number of overlays (pl 221). Single overlay bottles account for the vast majority of this group.
The basic ground colors of early overlay bottles were clear, white, or milk glass, sometimes with inclusions of fine bubbles called camphor, snowflakes, or snowstorm ( 193, 198). Bubble-suffused glass, also ranging in opacity from clear through milky white, would contain inclusions of such "snowflakes."
Tradition holds that red and blue overlays on a clear ground were the first to be made. The National Palace Museum in Taipei also notes that "the bottles made during the K'ang-hsi reign were all simple and old lokking. There were red and blue overlay which were commonly known as the Thirty-six T'ien-kang. There were also green, black, and white overlay on a blue-green or black background. Blue was overlaid on a red ground, but that type was rare. the carving was all of unparalleled refinement." Multicolored overlay bottles were made later, probably after the middle of the eighteenth century.
In evaluating an overlay bottle, the color and the smoothenss of the background are the true determinants of quality. The carving of the background, the innermost layer, represents the most difficult part of its creation, requiring skill, much time, and tedious work in order to reach among the spaces of the overlaid design those areas that must be smoothed completely and polished perfectly.
Multicolored Overlay Glass BottlesIn mulitcolored single-overlay bottles, the colors are applied in blobs by the use of tubes or sticks, each comprising a glass of a different color. The several areas of glass are carved in cameo style (222, 234, 237). While collectores seem to be awed by the extraordinary use of five to eight or more colors on a single bottle, applying the colors is not a unique or a difficult technique. Hre again, quantity is not as important as quality of color and skill of workmanship.
Yuan Chia Pei and Hsin Chia PeiSnuff bottles were made in Peking in small, private glassworks and family concerns as well as in imperial factories.
One often notes small black specks of carbon trapped witghin the glass of these bottles, supposedly introduced because they were fired in small family ateliers, where ashes might fall into the molten glass. Purportedly, the colors in their glass were achieved by adding pulverized semiprecious and preciouis sntoes, such as rubies, sapphires, and emeralds, to the molten raw material (253).
Seal-Type Overlay Glass BottlesSeal-type overlay glass bottles are attributed by Moss to the period beginning after the middle of the nineteenth century and lasting well into the twentieth (235,236,238,239). What remains to be learned of this large, select, and important group of bottles is beyond the scope of this chapter. Obviously they are not from a period when glass making was under imperial patronage, for the bear names and seals of craftsmen and ateliers that woul not appear on objects made in the imperial workshops, where only the seal of the emperor would be used. Some think that these bottles may have been produced in Yangchow.
Classification of artists' names and seals, hallmarks, studio names, and other aspects of these bottles warrants more thorough study. the workmanship usually is superb, especially in the double and even triple overlay examples (215, 221). the overlay is thinly applied in the desired areas of design and as a rule is delicately and finely carved in cameo style. The apparent firm degree of competency and sophisticated style of these bottles indicate a pride in workmanship incompatible with anything of lesser quality. While crudely made bottles are rarer and may sometimes bear the same seals, I (Bob Stevens) concluded that they are later, even contemporary, attempts to copy earlier examples. It is also possible that they represent the beginning or an intermediate stage, before a workshop's techniques were perfected.
Collectors enjoy looking at illustrations of others' bottles that seem to be identical with their own except for myriad tiny details, shich become inimportant in the light of the slight similarities. The glass bottles below are good examples. Despite the fact that there is not the slightest similarity in their designs, the bottles are so "alike" that the same master craftsman might have made both. At such times, most collectors enjoy the thought that rushes forth: "I must say, I prefer my own" or "The one in the book may be better, but I like mine more."
Few early glass objects made in China are large. Therfore glass bottles may well offer the researcher in glass the most fertile field for study.