I took a longarming class from Jamie Wallen. He said he doesn't understand why people keep coming up with new marking tools when there are perfect ones already available. He uses Bohin white chalk markers on dark colors and blue Mark B Gone pens (or similar brand) on whites. He says never ever use a Frixion pen because the marks can come back with changes in temperature or pressure. On the other hand, I took a class from another instructor the next day and she uses Frixion pens.