Caithness are rather fussy about quality control, if this is Caithness, it is likely a second - the interior colour is decidedly squint.
It can be hard to tell these from the wfs ones, Caithness ones do not have flat polished bases, but a curved indent from a mould. The edges of the polished rims are not sharp, but nicely rounded (I've got one sitting here beside me).
P 27. of Mark Hill's Caithness book shows a sandblasted one, and the caption says it was designed by Charles Orr. It is early - '60s ish, but they are quite common and are often mistaken for wfs ones. No actual date is given.