SPECIAL DOUBLE PORTION L'KAVOD SHABBOS KODESH

Halachos for Erev Shabbos Kodesh

1) A utensil that  varies in how it is used (i.e. it is sometimes used with boiling water and other times for roasting and sometimes for cold uses), according to the Psak of the Bais Yosef it requires Koshering based on how it is used the majority of the time.

Thus, for Sephardim who follow the Bais Yosef's rulings, if  a utensil is used mostly cold and occasionally for cooking, it would only require a thorough washing in order to  Kosher it. (See Shulchan Aruch Orach Chaim Siman 451:6. See also Kaf HaChaim 451:107 that this applies as well to Koshering for Pesach. He quotes the MaHaram of Panu Siman 96 that this Halacha applies even if one knows for certain that the utensil was used for forbidden food. See Chazon Ish Orach Chaim 119:15 and Mishna Berura Siman 451:46 for more details about this leniency)

2) However, Ashkenazim who follow the rulings of the Rama maintain that the Koshering method can be determined even by a minority use, require Koshering in boiling water in all cases. (Rama and Shulchan Aruch HaRav Siman 451. See also Shu"t Chasam Sofer Yoreh Deah Siman 114 for some exceptions to this stringency of the Rama)

Halachos for Shabbos Kodesh

1) One who purchases or otherwise comes into possession of utensils that previously belonged to a non Jew, even if they were only used for cold uses,  should   Kosher them in boiling water, even if they will only  continue to be used for cold uses

2) These utensils should be koshered immediately and not even be used temporarily until they are Koshered [and Toveled].  (See Shulchan Aruch and Rama Yoreh Deah Siman 121:5 and Siman 122:10)

This Koshering should be done before they are Toveled in a Mikvah.

If they were mistakenly Toveled first before koshering them, they should be re-Toveled without a Bracha. (Shulchan Aruch Yoreh Deah Siman 121:2 and Shach S"K 5.  For more on this see Aruch HaShulchan 121:9 and Pischei Teshuva 121:3)