This is a beautiful hand painted add-on cachet created by L. Ziola Powell.  It was skillfully painted with watercolors.  Although it is an add-on cachet, It's still one of my favorites.  It features the image of a doctor or scientist with some test tubes and some kind of scientific looking design on the wall.  Not being a scientist myself, I don't know what, if anything, the design represents.  If you can explain it, please let me know.  The example in my collection is number two of only three made.  I don't know for sure when the cachet was added to this cover, but I don't think it was done recently.  The paint looks to me to be rather old and slightly faded, however it is difficult to be certain.  If you are able to provide additional information about this cachetmaker, please drop me a line at smith@in.net.