I have been wearing tekhelet for about a year now, and I would like to start off by thanking the Ptil Tekhelet Organization for helping to revive this mitzvah. I have a question as to the length of the tekhelet string on the tzitzit. Is it kosher for the tekhelet string (I wear Rambam tekhelet, so there is only 1 string) to be shorter than some of the white strings? If it is not kosher, should the white strings be shortened? Also, I heard that it is only appropriate to bite off strings, not to use scissors or a knife?
1) I am not aware of any white-to-blue relative length considerations. The halacha does talk about minimum lengths of strings of course (i.e., k’dei aniva), but this applies to all strings equally. So, in answer to your question, I do not believe there is any need to shorten your white strings in order to make your tekhelet appear longer.
2) The Mishna Berura notes (Orech Hayim, Siman 11, Seif Katan 61) that one should use teeth and not a knife. [Note that he does not use the language of “must”, so it appears to me that it is preferable to not use metal, but not an inviolable requirement. That being said, we employ special ceramic scissors in order to fulfill this recommendation].
– Mois Navon.