This Extra Large mug in Speckled Cobalt blue is colored with several oxides including Cobalt Oxide. This deep blue glaze is speckled with larger particles of cobalt which have not fully entered the melt. I really appreciate this speckling effect and feel that it adds so much to the final product that would be missing if the whole glaze was uniform. Its this variation in handmade pottery that I adore and hope you appreciate too. The Volume and comforting character of this pot win over the big mug tea and coffee drinkers especially.