N.B. Glass Works Perth Glass Target Ball.  This target ball is from England in the 1875-1900 era.  Vivid, very deep cobalt blue, quilted diamond patter above and below center band, 3 piece mold, rough sheared mouth, dia 2-5/8".  Note, mold with backwards "S" in "Glass" and "Works".  Upside down P in "Perth".  The NB stand for New British.