As I came across this post where Etling and Verlux were mentioned, I just wanted to share my thought and finds on this subject.
I have done a little digging or quite some rather and it took me a while... hence the late reply.
Cappa, as you all know, mentions in both of his volumes that Verlux relates to Etling. But as the French language can often be so subtle in its wording, you need to really pay attention, because often it's very suggestive.
And that is exactly the case here, because in his first edition, Cappa says that Verlux could be related to Etling because a pinecone patterned vase has a very similar pattern to a bowl (the square one I guess) by Verlux. If you're happy with that, then that's fine but personally, I find this a little vague and not evidential enough.
Hartmann mentioned on several occasions, at the SPIP and Verlys references, quote page 813 ' The establishment SPIP proposes art glass, Cristal and decorative objects made from different materials, in 1935 the department store SPIP officially registers at the Chambers of Commerce, the brands Verlux, SPIP and Vermer.
And also : 'The glassware Verlux was produced at Hollophane - Andelys, the brand SPIP with the subscription Tchechoslovaquie was imported (by Inwald) and the producer for Vermer is currently unknown (but due to style it could be Schneider or Daum).
Page 858 on Les verreries d'Andelys he mentions that 'the company starts producing décorative pressed glass and lamps in the Lalique style. Verlux is produced for the proprietor of the SPIP establishment, Paris, Rue de la Grange-aux-Belles 39.'
Overall in his book, Hartmann refers to Cappa on several occasions, so he's read his views but ignores him on Verlux. In Cappa's second edition, he refers to himself in his own first edition, whereas Hartmann still ignores this suggestion.
The reference on SPIP from Hartmann, comes from the Commercial Syndicate Register for Ceramics and Glasswork, dating from 1930 and onwards.
It took me several hours, on the french online library Gallica to find out who this etablissement SPIP was, also where the Verlux name was registered, and I found it in the end.
SPIP was a department store, very much in the style of Sabino and Etling, and like so many others. It stands for Société Parisienne d'importation de Porcelaine. Why porcelain? Because that's what they started their business with and they expanded their range with glass, Chrystal, decorative objects and the likes as of 1935, after having been 5 years in business.
Also, for the brands Verlux, Vermer and SPIP, Hartmann refers to the 'le bulletin officiel de la propriété industrielle et commerciale Paris - 1886-.... the official report on industrial and commercial propriety and patent.
Personally, and these are just my thoughts, is that the theory suggested by Cappa, is exactly what it is...a myth that slowly made its way in because of Cappa whereas Hartmann ignores these and comes up with evidence that Cappa doesn't have. If Hartmann refers to both registers, then he must have consulted them.
Verlys, as we all know, was Hollophane's own trademark for decorative glass.
Underneath, you'll find a copy of the announcement for the establishment SPIP having been registered by proprietors Guerber et Broido, dating from the 1930 register.