Mengrai Kilns ROP. specialize in making hand crafted art Celadon and other Stoneware, using as far as possible traditional materials and methods. It is not always possible to get each piece 100% level.
  Ref : TURQUOISE COLOR : This color has more absorb in pecentages and can absorb oil that has change in color a little bit, same as the other color such as Ivory color will have black stain of caffeine in the crack. Turquoise color is warranted free of Lead and other Toxic substances. We have already test for toxic from them. Please see our Certificate that has shown there do no Lead and Toxic from this color after touching the oil and microwave.
  If you mind about the changing in color of Turquoise after touching the oil or stains from the food, please do not take them, we quite under stand about this.