Unfortunately, 'dumps', often those with complex interiors seem to have been produced more recently than the Victorian period - some are in exceptionally good condition.
The answer as to why use glass to keep the door open may relate to many similar situations where something which once had zero value and considered only of immediate utility use, was commandeered into service as the first heavy object to come to hand and which did the job.
These dumps originally had none of the antique value they now possess - look how much of our history we binned 1850 - 1950 before we realized the past was interesting and valuable.
how about an industrial sugar crusher? If you look at the much smaller sugar crushers used when making hot toddies in rummers, they had a similar domed head, which became worn with use - though these are not I don't think what we now call stirrers.