I have been doing some reading about stained glass cement products and recipes and have come across comments that cements or glazing compounds containing Portland cement and/or plaster of paris should not be used. I have looked up some recipes for cement that contain portland cement and plaster of paris and some that consist of only whiting mixed with the liquids and colourant. I have tried the one with only whiting but find that it will flake away or turn back to powder if picked at. My question is, should I be staying away from recipes with Portland cement and/or plaster of paris or are they required to make a proper and effective stained glass cement?