Choose 2 negatives that you feel will work well together and produce an interesting effect
Place these 2 negatives together in the correct position emulsion to emulsion in the negative holder
Fix them in place using clear tapeĀ
Test in the usual way but double normal time strips to 2,2,4,8 seconds to give you 2,4,8,16 seconds to look at
Develop, stop and fix in the usual way.