Hi from Paris,
Lodz was a large industrial and modern city mostly involved in textile manufacturing to Russian market.
This market was lost after WWI (due to German occupation, 1916, then Bolshevik Revolution, 1917, and last but not the least, by Soviet-Polish war, 1919-121).
In 30', one third of Jewish population was living on welfare.
Due to its size, Lodz' "yellow pages" directories (of course whithout phone) were edited as early as 1900 to help people to find who and where they could contact for business.
Lists are sorted by kind of activity, then names.
You can find some shops & business ads within these directories.
Last directory was 1937-1939.
You can find them at
Enter your parents' name and place of Lodz to focus your search.
You download full scan (all pages) of these books, then look at indexed page with your "names".
Another important data is available in Lodz, as this city hadn't been destroyed during WWII and all archives (including vital records, ..) are available.
During interwar period, each shop, each company had to be registered to get authorization to do business.
So you could get copy of business registration file of your GGF.
To get mine (an Irish pub in main street), I was lucky to be connected to a local genealogist specialized in Jewish genealogy.
She could find these copies ... and all my vital records from 1850 to 1939.
An astonishing conclusion: these companies had not been closed by Shoah and were still registered after WWII.
In early 70's, Polish administration sent official letter to their address: as nobody replied (...), they closed the registration!
Archives & history of Medem Center - Arbeter Ring (Bund, Workmen Circle of France)
Searching ZYSMAN, KRONENBERG, ROTTERSMAN in Lodz