Westerwald Salt Glazed Antique Tankard / Pitcher

I found this pottery piece at a local thrift store and would like to sell it but would like to be accurate about what I am selling.  My initial research tells me that it may be a pottery piece by Westerwald, and is salt glazed pottery.  I am interested in knowing the age and approximate value of this piece.  It has a no. "1" etched into it by the handle and has a pewter hinged lid.  It is in very good shape with only a tiny pin hole sized dent in the lid and a tiny chip but I otherwise cannot find any major flaws. 

It is grey in color with cobalt blue flowers, and a swirl pattern on the bottom.  Other then the engraved no "1" I do not see any other identifying marks.