I am by no means an expert on Korean glass, and I won’t claim to be one here. I also haven’t looked at Korean glass as much as other regions, so please take this as a general summary rather than an expert account!
Some of what I summarize here is taken from articles I’ve read and will include below. Other information comes from conversations with James Lankton that aren’t really recorded anywhere. Most of this info is about 4 – 5 years old, so there may be things we didn’t know before or things we thought we knew that we really don’t anymore.
Most glass research in the Koreas (we are talking predominantly South Korea due to the political situation in North Korea) focuses on glass beads rather than vessels or other glass objects.
Research on Korean glass covers sites across the peninsula and also into parts of Manchuria. The sites discussed generally range from 200 BC to AD 1200.
There’s lots of discussion of mosaic cane manufacture, since certain types of Jatim beads have been found in areas of Korea. This manufacturing technique uses a cane, or rod of glass that is generally a single solid color (often referred to as the matrix). Slivers of different colored glass are then applied to the original cane in a specific pattern (such as eyes, swirls, birds, faces, etc.). The bead is then reheated so that the appliqued glass will even out, forming a single, round, highly colorful and decorated bead.
Five chemical groups re mentioned by Insook Lee: lead-barium silicate glass, lead-silicate glass, potash glass, soda glass, and mixed alkali glass (soda and potash). The two lead-based glasses are similar to types found in China, and the lead-barium-silicate glass seems to be the earliest glass found in Korea. Potash glass was introduced around the first century AD, while the lead-silicate glass appeared around the 4th-5th centuries AD. Soda glass and mixed glass do not have dates given in the literature for their potential introduction. The potash glass is often seen as Chinese, but there are significant differences between Korean potash glass and Chinese potash glass, suggesting that it may actually originate somewhere else (e.g. Korea, Southeast Asia, or elsewhere). Soda glasses are often associated with Southeast Asia, primarily Thailand. The chemistry of the Jatim beads is not given.
The fact that most beads in Korea were found in royal or noble tombs signifies that these objects had acquired a special status. In China and Southeast Asia, glass beads are most often found in burial contexts, though the same cannot be said for South Asia or many other regions with glass beads. Japanese glass also seems to appear primarily in burial contexts, suggesting a separation between East and Southeast Asian uses for glass beads on the one hand, and South Asian, Islamic, Egyptian, and Roman glass object on the other. Alternatively, this difference may occur due to the focus on glass beads in Southeast and East Asia, but the difference still holds for South Asia at the very least.
Almost all beads in Korea are either a mosaic type or a shade of translucent blue. There are certainly exceptions, but this seems to be the general rule. The uniformity of color is interesting, because we generally do not see this uniformity elsewhere (save for Japan). This implies that the beads themselves served a specific purpose and that the color of said beads was central to their use. In other words, there was a preference for these two styles in Korean nobility. The purpose of this preference remains unknown, but it is worth noting here.
Another point of interest is the presence of Jatim beads in Korea. Jatim beads are a name given to a group of specific bead styles found primarily in Jawa Timur, or East Java. They include bird and star beads, certain opaque yellow beads, mosaic cane eye beads, and certain combed beads. Outside of Java, their presence seems limited to parts of Korea, though one bead has been found at Berenike, Egypt. The distribution of these beads is interesting, because they are not found anywhere save for these three, very far removed locations. It also points directly to trade relations between Javanese manufacturers and Egyptian and Korean consumers. Both these points seem to imply that certain Korean trade bypassed other major super-powers (e.g. India and China) in order to trade with other groups that were further away.
The chemical composition also necessitates mention, because these chemical groups show a connection to both China and Southeast Asia. Given the connection of the Jatim beads, it is understandable that Korean glass would be compositionally Chinese or Southeast Asian. Yet, there is evidence that certain Korean beads are connected to Thailand as well, not just Java. There is also little evidence of local manufacture in the literature, meaning that glass in Korea was, perhaps, a strictly imported product. This might help to explain its elite status, as well as the uniformity of colors and styles.
Francis, Peter J
2002 Asia’s Maritime Bead Trade: 300 BC to the Present. Honolulu: University of Hawaii Press.
2009 Characteristics of Early Glasses in Ancient Korea with Respect to Asia’s Maritime Bead Trade. In Gan Fuxi, Robert Brill, and Tian Shouyun, eds. Ancient Glass Research Along the Silk Road. New Jersey: World Scientific. Pp. 183-189.
Lankton, James W, Insook Lee, and Jamey D. Allen
2003 Javanese (Jatim) Beads in Late Fifth to Early Sixth-Century Korean (Silla) Tombs. Annales du Congres de l’Association Internationale pour l’Historie du Verre: 327-330.