I'm afraid that your
lamp is almost certainly a modern
fake made in
Bulgaria. These are commonly artificially aged (often extremely convincingly) to pass them off as originals.
The clay and simulated slip are typical of the
type and become instantly recognisable after handling a few examples. The wide flat shoulder and plain base are also common features (though not invariable).
I'm sorry to note that these
Bulgarian fake volute lamps have saturated the market in the past few years. They have often fooled even experienced dealers and top auctioneers, and examples crop up everywhere.
A colleague of mine deliberately ordered a few of these directly from one of the makers in
Bulgaria in order to familiarise himself with them. They do become instantly recognisable after awhile.