Date a fairly medium dating

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The purer the sand (i.e., the higher the silica concentration and less iron) the better, as it is the other impurities - desired or undesired - that give glass its color.

Low iron means more control over the ultimate color (Hunter 1950; Tooley 1953).

Bottle colors also warrant coverage here simply because they are of fascinating interest to people.

As implied in the quote above, there are some time related trends in color that can be of utility for dating. The specific "diagnostic utility" of a given color is noted in the descriptions below.

There is a very broad chronology of popularity of various colours over time; however that chronology cannot be applied to individual glass objects with any significant level of meaning..."The majority of common bottle glass is "soda-lime glass" which is primarily composed of silica, soda (aka soda-ash) or potash, and lime - the latter two ingredients often referred to as the "alkalies" (Hunter 1950; Toulouse 1969; Munsey 1970).

The silica (silica dioxide) typically makes up 60-80 % of the glass composition and is primarily derived from sand.

Although classification by colour is simple to do, the end result is of little value for the following reasons: colour does not have a direct relation with glass type (the common green, amber, and brown glass colours can occur in soda, potash, and lime glasses; many lead glasses are coloured); colour is not related to the technology of glass object production (i.e., it has nothing to do with whether the glass is free blown, mould blown, pressed, or machine made); colour is only weakly related to the function of the object (almost all colours can be found in all types of objects, an obvious exception being "black" glass which does not occur in tableware).

Having quoted this, color is still an important descriptive element for the recordation and classification of 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.

This is done by adding certain types of compounds to the glass batch in certain quantities.

Bottles made from glass with just the basic ingredients (sand, soda & lime) will usually be different shades of green because of the iron impurities in the sand, though other colors can also be attained depending on many factors.

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