To be added to the beginner's collection. These are two different papers that saw use in non-overlapping time periods.
The 25c 'Servicio Oficial' clay was not issued as a regular stamp. The blind perfs tell us that this paper was too thick for the perforating machine.
Clay 30c from 1930, a somewhat scarce stamp. The paper is very thin and tears easily. A good 20 pecent of all of these stamps I have seen on cover have a major tear, usually a whole corner missing!