Due to the space limitations of a text message, please note that it is particularly important to read carefully, pay close attention to the context of the question, and use the answers as a springboard for further study.
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Q: May one apply clear lip gloss on Shabbos?
A: Colored lip gloss is considered like painting and therefore not allowed. Rabbi Shlomo Zalman Auerbach was of the opinion that even though clear lip gloss doesn’t change the color nevertheless since it creates a shine and brings out the original color it is also considered like painting (tzovea), just as one may not apply oil to shoes on Shabbat for the same reason. There may be opinions that are lenient but to the best of my knowledge they are not well documented.
Q: Can ceramic plates be kashered if they were fully non kosher before?
A: It’s best to get rid of them and buy new ones. If there’s a compelling reason to keep them, they should be immersed in boiling water, then again in fresh boiling water, then a third time in fresh boling water (Iggrot Moshe 2:46). This should ideally be done after they were not used for a year.
Q: I just read online that some beer is not acceptable for vegans since it is filtered with fish gelatin and trace amounts of it inadvertently remain in the product. Does that create a kosher problem if the gelatin comes from non-kosher fish? I thought all plain beer is kosher?
A: It is still kosher – first of all, the gelatin may not be from non-kosher fish. Secondly, it is nullified since the amount that remains in the product is negligible.
Q: On Friday night, is it permitted before Shabbat begins to leave fully cooked food to stay warm in an oven that is turned on and then remove it for dinner after Shabbat has already begun?
A: It is permitted to open the oven to remove the food as long as an oven light doesn’t turn on when the door is opened, even if the heating element is eventually activated by the cold air that is let in (Iggrot Moshe OC 4:74 Bishul 8 but see R. Jachter’s article entitled “Opening Refigerators on Shabbat” ).