Some questions were asked in regards to glass dishes. Is it permissible to use glass dishes on Pesach if they were used during the year? Is it permissible to use glass dishes for both meat and milk?
The Ashkenazim hold that glass has a status of Keli Cheres, which is to say that glass dishes are equal to that of pottery. So according to Ashkenazim, glass dishes absorb flavor just as pottery does, and therefore Ashkenazim do not allow glass dishes that were used all year long to also be used on Pesach. This is also the opinion of the Ben Ish Chai, who held that one would have to pour hot water over glass dishes in order to kosher them for Pesach use.
However, Maran is clear, and most of the Tosafot are clear, and they hold that glass dishes do not swallow and are not considered like pottery. Everything slides off glass, and therefore according to Maran and many of the Rishonim, it is permissible to use everyday clear dishes on Pesach. One must make sure the glass dishes are clean from food, but Hagalah (placing into pot of boiling water) is not required, and Iruy is not required (pouring hot water onto it.) This would apply to Pyrex glass oven platters that are clear, or to any other type of glass vessel that is clear. They can be used for Pesach.
Now even though Ben Ish Chai is strict on this for Pesach, he however does allow glass dishes throughout the year to be used for both and milk. (Of course this is referring to using the dish for meat and milk separately and not together at the same time.) By Pesach he is strict because of the restriction of Hametz. But milk and meat during the year is permissible. Even by the Ashkenazim, glass is permissible for meat and milk.
We all have separate dishes, and Halacha does advise to have separate dishes for meat and milk in order to avoid mistakes and problems. But, in a situation where we have a glass dish, or in a case where you are away from home in a hotel or condominium which has glass dishes only, it is permissible to use these glass dishes one night for meat and the next night for milk. And for Sephardim, these glass dishes can even be used for Pesach.
Again, we advise to have separate dishes in the homes, and not simply have one set of glass dishes for universal use. But Halacha Lema'ase, it is permissible to allow clear glass dishes to be used for both meat and milk, and for Sephardim to be used for Pesach even without any hot water koshering process.