Note: Russian silver was made using the Zolotnik system rather than the English sterling or western continental standards. There were three standards: higher , medium and lower as was also the custom in some of the continental western countries.
84 zolotniks = .875 silver
88 zolotniks = .916 silver
91 zolotniks = .974 silver
sterling = .925 silver
continental European silver is typically .800 or .900 silver
The lower 84 standard (these spoons) is below the sterling standard, but is higher than the 800 standard which was used in most western continental countries. The higher standard (91) was much purer than the sterling silver standard but is not found on flatware because it is too soft for normal use.