A Cobalt Blue Sea Glass Bottle Bottom

The cobalt color was achieved by adding cobalt oxide during the molten stage producing varying blue hues in the glass depending on the amount of cobalt added. Cobalt oxide has been used to color glass as far back as the early Egyptian and Roman times.

Cobalt oxide has been used to color glass as far back as the early Egyptian and Roman times.

Due to the desirable blue color and its wide use in bottle making, it can be difficult to date cobalt sea glass unless there is evidence of unique, identifying markings. Most thinner cobalt shards are from the early to mid 1900s when bottle manufacturing increased for the companies mentioned earlier.

Some thicker cobalt sea glass can be attributed to soda and mineral bottles that were blown in the 19th Century. Other possible sources of cobalt sea glass were poison bottles, ink wells, apothecary jars and bitters bottles.

The cobalt blue color found in sea glass has always been valued by the sea glass collector just as with bottle collectors and manufacturers wishing to make their product stand out. Consider yourself very lucky these days to find such a beautifully colored sea glass gem as it is getting much more difficult to find.