Trying to figure out this glass process

[alan giberson]

These signs we in Cleveland's Union Station. I am trying to figure out how they were made. The textured part does not seem to be acid etched, but more like the texture on some stained glass. The glass itself has a ochre color to it. They were backlit, with light shining through the letters. The negative space is blacked out but also has a texture to it. The back of the signs are all clear, bare glass - all the work done on the front. What puzzles me is the tiny raised outline (see on the letter A, which the photo is upside down). From the back, the letters are raised from the negative space or background - the background was etched or blasted deeper than he letters.

Any help would be appreciated, as I am to restore these signs as similar as possible.

All of these signs were in a fire in the early 1900s

[pat mackle]

I have the answers for you on these signs. I replaced the same type of back lit glass signs to replace the broken ones in The Union Station in Los Angeles, California. I did them when I was in my previous shop back in 1993. They were for the Western Union booth areas. Your panels in your photos are done on amber colored "granite textured" glass. It was a widely used glass choice for signs and lighting fixtures in the 20's through the 40's.Not as easy to find it today. But you may find a suitable match. The front side of the glass has had the background sand blasted to indent it and paint filled with an opaque metallic bronze paint. The letters were masked for protection from the blasting prior to sand blasting, and the masking then remained on the glass while the metallic paint was applied. It may have been brushed or sprayed, and was intended to be dense enough to block out the back lighting. I suspect that through many years of service, that the metallic paint has changed color as it became weathered and oxidized.
To get similar results, you must use a genuine "sand" abrasive to get the same "pebbled" blast finish. You CANNOT get that with aluminum oxide or silicon carbide. They will not "pebble" the glass. Back when these signs were made, silica sand and garnet were the chosen abrasive medias. Sometimes on these signs you will find that colored acetate films were sometime added to achieve a specific color to the glass.

[John Smith]

wow - very interesting project !!!
Pat, what do you think was used as the sandblast resist back then ?

[alan giberson]

Pat, I hope you'd chime in on this. Thank you very much for the info. I think I can get good headway on this now.

Off to try and find some amber colored glass...

[pat mackle]

In the early days of sand blasting, various things were used to create something that would protect the glass from the sand. Almost immediately, inventive processes were dreamt up by tradesmen to save time on duplicate designs. India rubber, and thick parchment stock soaked in varnish were just a few. Lead metal foil adhered with soft wax was another. Animal glue with additional ingredients to make it rubbery were also used. And there were several more even more creative ways developed in time. There was even an early photo resist process in those days. Many early resists just barely protected the glass. This weak style of resist is apparent in early mass produced etched 'scenes' in which "over blast" can be seen in the clear areas. It appears the etchers were able to sell them even with the obvious flaws.

[John Smith]

Thanks Pat - very informative indeed !!
I have only done a handful of dimensional glass projects and am
mezmorized at the sharp serifs on each and every letter !!!
I don't think I could not achieve such accuracy using computer cut mask.
and of course, all that work was done FREEHAND with no Duct Tape !!

I just think vintage glasswork like that should be preserved - no matter the cost.
our present day pioneers such as Rick Glawson and others are a Godsend
to preserving yesteryears craft for todays craftsmen.

Thank you again for sharing your knowledge.



.

[Kent Smith]

A bit more trivia to tie into Pat's information. Although railroad related blasted glass would usually be attributed to Western Sandblast Company in Chicago, Cincinnati Sand Blast Company was know for architectural work in addition to their beer advertising signs. The letter style and lack of perfection is often seen in the work from Cincinnati.

My opinion because of the impact texture on the letter surface, I would suspect parchment resist.