Hi Ken,
For a brief mention of the work of Michael O'Keefe, see The Art of the Paperweight by Lawrence H. Selman (1988). The colouring and general effect of those weights was achieved by a processs called "silver veining". O'Keefe's work was said to be reminiscent of early work by Dominick Labino - another name to check out.
Although my main focus is on older Scottish weights, I would like to have some examples of O'Keefe's weights as I think they were amongst the best of that type.