I purchased a non-photo blue pencil several months ago (made by Staedtler) in an arts and craft supply store. Don’t know if it is the same as the one offered by Gaylord or not. It did not help. Lately I read that “non-photo blue” is the name for a shade of blue… because it does not photocopy good in gray tones. I’ll bet the one I bought was just an ordinary everyday colored pencil.
A few days ago I found prismacolor brand pencils at a small non-chain arts and craft store that also sells a few “archival” products. I took one of our photos with me just to see how it worked. The non-photo blue worked, but it was too light in color. I tried the black (#PC-935) and it was legible. I bought two of them. I think I’ll go back and also buy the non-blue for those times when we have a photo with original writings on the back of a photo.
The non-chain store also had the woodless pencils made by Koh-I-Noor, but they had 12B; not 9B. The 12B was too soft and I had to make my letters big.
Thank you for your input.