Greensboro crocks a cash collectable

My wife's grandfather coal miners from Greensboro, Pennsylvania. It is a very small historic town on the Monongahela river in southwestern PA.It is about 60 miles south of Pittsburg. Beside coal mining the other big industry in between 1850s and 1915 was making stoneware pottery. Since the plant was right next door to my wife's grandparents house, she has sentamental intrest in collecting Greensboro pottery. We have two sizes from a gallon size to probably the largest they made a 15 gallon size. They are gray on outiside with navy blue lettering and the Greensboro PA on the front in large letterings. One sign of it being a genuine antique pottery is on the inside surface the feeling of the glazed in coal dust.The large crock has some cracks but my wife got a deal given it ideal condition it could be worth over 5000 dollars. Greensboro crocks have become very collectable in the last twenty years.