Helen- I haven’t had much luck enameling on PMC, but I know Pmc much
better than I do enameling. One thing caught my attention in your
post. I believe that PMC (PMC+ should be somewhat less) absorbs
tumbling solution. This causes Black Max, for example, to come out
yucky grey at times. You might want to consider not tumbling, or
tumbling a second time, briefly, with plain water, or at least rinsing
very well, and then allowing time for the water in the PMC to
evaporate fully.It seems possible to me that some residue from the
tumbling could influence your enamel. Or, maybe not! Good luck!
–Noel