There is only a small mention of Britzin in the standard work "Russian Gold and Silverwork, 17th-19th Century" by Alexander von Solodkoff (Rizzoli, 1981).
pg. 116:
Between 1870 and 1917 Ivan Britzin had a workshop which exported articles to Western Europe and America. It specialized in guilloche enamel and produced in particular picture frames, clocks and watches, cigarette-cases, and powder boxes, mostly mounted in silver. Very few examples of gold work by Britzin are known. His palette in enamel was simpler than that of Faberge, being confined mostly to pastel shales of light blue, violet, and grey, with white also. It has been suggested but not proved that Britzin was apprenticed to Faberge or worked for him. While Britzin seems to have been Faberge's leading competitor in quantity of production, in quality it was the jeweller Hahn.