You may wish to look at Phoenix Art Glass, Leland Marple, 2004, Schiffer Books, Pg. 71, Plate 177. This diamond within a diamond pattern appeared in the May 1885 issue of Crockery & Glass Journal in the form of a flower basket which is identical to pattern on the pitcher shown in the Phoenix book. Phoenix was located in Phillipsburg (now called Monaca, PA) & it is generally accepted that this pattern in this MOP configuration is Phoenix & your piece bears a strong resemblance to the pattern, however I would recommend the compare the two side by side & make your own conclusion. Note that I would not make this recommendation on most pieces of this pattern, only the MOP configuration which appears to be the same (pattern & color) as found in the Phoenix reference. A photo of a ewer I have with this type of pattern is below, however this is not Phoenix because it is simply opalescent.