All this talk about Jantex rim tape and rims reminded me of the "Record Duralium" sprint rims. These were super light and had a specially roughened surface for better tub adhesion. The advertising blurb called it a special granite surface. These were very popular in the 30's and were still readily available throughout the 50's and into the early 60's.
Best wishes and be lucky. Michael Butler Huntingdon UK.