Jostra were makers pre and post war, it's the firm of Joseph Traut It had different names later on.The glasswork was all made inhouse (if you include pieceworkers in the town) with local glass. No importing, lots of exporting. He was a Master glassblower like most of his brothers, one of whom went on to start a global glass company a world leader today. A good place to start is Heinrich Geissler a very important historical glassblower.
This is corroborated with, catalogs, adverts, order cards.
Finding out someone I would need to speak to was quite poorly.
Jumping on a plane hiring a 4x4, collecting a stranger I met online.
Interviews with workers and the children of workers.
Visiting the archives in local museums.
Reading newspaper reports of their work.
Reading academic articles about the family.
Actually banging on doors.
I'm not sure if confirmation from me is what you want, I think you want to know what's right but with my handful of posts what I say bears little weight and would be difficult for you to confirm without the background information, which would also be uncorroborated if it came from me.
My research is on Glass Cocktail Umbrellas, that's what I love and why I ended up extensively researching Jostra.
My research background, I trained as a scientist, Studied history so understand the basics primary secondary evidence etc, and spent a number of years working as a global corporate structure investigator specialising in x-border companies.
My research background in glass is zero.
Dominic