These were made by Fred Locke at the victor plant and come marked Murdoch pat They come in a large and small disk size and are normally white glazed Most all of them I have seen came from the Victor dump [id=305391059] to see two of the small size found in Victor. These have the same filed firing rests as other Fred Locke insulators and come in the same grayish white color as Fred Locke pintypes . there is a report of a single brown one but I have not seen it. The larger size is very rare with the murdock incuse marking but all the smaller ones come with the marking.