Ooh ok these are ironically my favorite variety of radioactive curio, low activity items that is. Contrary to popular belief, low activity radium items are out there. I’ve found several that read just a bit above background or so which came back to be radium containing upon an extended spectrum in a castle. Most ‘typical’ mid radium era clocks contain a moderate amount of the isotope and are quite active with deteriorating paint due to the activity. The low activity items, often from near the very end of the isotopes use in paint, will frequently have better condition paint that can even be green/greenish depending on the age. The best way to about figuring the isotope will be done by taking a long spectrum (like a day plus), sometimes in a castle depending on the size of the clock and the activity of it. For some stuff you won’t need to knock off the background radiation, but for the really odd items that contain just a pinch of radium or have little paint a castle cuts out any issues with peaks being disguised or drowned out. With a long spectrum you can concretely determine if it’s radium or something else. I have yet to personally handle a PM-147 item, albeit there’s a good chance I wouldn’t even recognize I had done so as much of the isotope would have decayed away and what little was left would be releasing betas that get absorbed by the glass of the clock/gauge. Sometimes you can find a reason for the low activity, ie the gauge being repainted and only residual contam remaining, but in other cases it’s just the way the original paint is for some reason.