Vintage Cristal D'Arques-Durand France Sapphire Blue Cobalt Glass Mugs set of 4

Vintage Cristal D'Arques-Durand France Sapphire Blue Cobalt Glass Mugs set of 4 embossed made in France. 8 oz. set of 4 3 3/4 inches tall. Cobalt Blue glass is not painted or coated. Cobalt blue glass owes its color to the addition of cobalt compounds, usually cobalt oxide or cobalt carbonate during the glass-making process which gives it deep, saturated color and subtle transparency.