In the book Paperweights, by Sibylle Jargstorf, published 1991, "carpet ground" weights simlar to the one son here (the book shows one with plain dome - dated as 1986, and one overlay type - dated as 1988) are atttributed to the former A. L. T. company in Murano.
A search for "ALT murano" in the board will find a few references inlcluding one saying that the two main men from A.L.T. formed the 3 Fiori company and made good quality weights (but the company also closed down some years ago. 3 Fiori also made "carpet ground" weights.