I understand that glass and ceramic are not kasherable but they still are by far the most convenient and least expensive materials for dishes and cups. If these vessels were purchased new-in-box, it would seem they would not need kashering as they made no contact with food yet. On that basis, may non-kasherable items that arrive in such condition be used in a kosher kitchen?
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*Re: last comment -- I am assuming this is a commercial or restaurant kitchen...– SAHMay 4, 2016 at 11:21
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Now, this is just for home. But we want to serve friends and guests.– eternalsquireMay 4, 2016 at 15:00
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Why was my first, much more useful comment deleted? sigh. @eternalsquire, the short answer to your question is "yes," they are kosher (and will remain so until used with non-kosher food, or meat/milk that they are not designated for.) Be sure to tovel the dishes before use.– SAHMay 4, 2016 at 18:13
1 Answer
There are two separate issues regarding kitchen utensils, dishes etc.
One is if they absorbed non-kosher food in the past. Since these utensils are new, this is not a problem for ceramics and glass. However, it may sometimes be a problem for some new metal utensils, such as pans, that may have been coated with non-kosher fat as part of the manufacturing process, and therefore will require kashering. See here, for example: Shaarei Halacha
Otherwise, it would only apply to second-hand utensils, dishes, glasses etc. that were previously used for non-kosher food.
The second issue is "toivelling" = immersion in a kosher mikva. Any metal or glass utensil that previously belonged to a non-Jew, must be immersed in a mikva (even if it was never used). Wooden utensils are exempt. Other materials need to be checked with a rabbi, since there is not always a halachic consensus (e.g. plastic, ceramics with a thin glass coating).
This seems like a good starting point, although other rabbis may disagree on some points.