Soda (sodium dioxide) - aka "alkali," "soda-ash," or "potash" in the trade (Trowbridge 1870; Toulouse 1969) - is added to the sand as a "flux" to lower the melting temperature of the silica.

Although color is one of the more obvious and relatively easy to describe attributes of a historic bottle, it is unfortunately of limited utility in classifying a bottle as to age or type.

One of the better discussions on this is from The Parks Canada Glass Glossary by Jones & Sullivan (1989), and is quoted below:"Because colour is a universal attribute of glass and is convenient for mending and establishing minimal vessel counts, it has been latched onto by some archaeologists as a classification device.

As noted on Greg Spurgeon's fruit jar oriented website there is no "governing authority" on glass or bottle colors (Spurgeon 2004).

(Note: Spurgeon's excellent fruit jar color information webpage is located at the following URL: There always has been and will continue to be confusion as to color nomenclature even though many attempts have been made to try to standardize it.

Glass composition formulas were (and probably still are) closely held glassmaker secrets as the experience of extensive trial and error experimentation in glass making was not readily shared with others.

Variations in glass color resulted from a myriad of different causes including the strata of the sand source, the mineral in the soil of the of the trees burned to produce "potash" (an "flux" alternative to soda), and many others known and unknown (Toulouse 1969a).In the following color descriptions, the different coloring (and de-coloring) agents or compounds for the different colors are briefly noted.This is just informational because the actual chemistry is of little utility and glass colors only contribute a little to the process of dating or typing historic bottles.For example, if one has a colorless ("clear") bottle which was de-colorized with selenium and/or arsenic which gives the thick parts of the glass a subtle "straw" tint, it very likely dates no earlier than World War I (1914-1918) and infrequent in bottles after the 1940s or early 1950s (Kendrick 1963; Lockhart pers. There are also some colors which where very rarely used for one type of bottle (i.e., cobalt blue for cylinder liquor bottles is very uncommon though do exist) but quite common in others (e.g., cobalt blue for poison bottles or Civil War/Antebellum era soda water bottles).Thus, some information can sometimes be gleaned from knowing what color is or is Simply put, people observe or interpret colors (or in Canada - colours) differently.It is, however, part of the overall "story" of bottles covered by this website.