Railroad Glass Colors and "Cobalt Blue"
by Paul Lubliner

When it comes to railroad lamps, lanterns and signal devices, they have one thing in common: the colors of the glass used in them. Sellers and collectors in today's railroadiana market have adopted certain terms to describe glass colors, but some of these terms differ from what railroads originally used. The biggest departure is the use of the term "cobalt-blue" to refer to a number of different glass colors. Below is a quick overview of the SIX Railroad Signal Association (RSA) 10-10-1905 sanctioned railroad signal glass colors.

Railroad glass was originally designed for the lamps, lanterns, and signals that used orange-tinted combustible fuels, and early glass manufacturers produced a rainbow of colors and color variations for individual railroad's preference and use. However, the early years lacked standards, so that, for example, blue-hued glass lenses and roundels -- seemingly identical -- conveyed colors ranging from greens to blues to violet. As an aside, roundels are optically plain glass, meaning they neither magnify nor spread light (or refract) as do lenses; they only permit the light passing through to be given a specific color to convey information.

The greatest obstacle to night indication safety was directly due to the 1841 agreement made in Birmingham, England where the use of red for stop, green for caution (later "approach") and "white", actually plain and untinted flame for "clear", was adopted and sanctioned. Early U.S. railway signal practice closely followed that of the U.K.'s.

The purpose of all railroad lamps, lanterns and signals was nothing less than the protection of people's lives, but glass colors were yet unstandardized, and this created ambiguity and worked against safety. The danger lay in the unavoidable breakage of a given red glass roundel or lens falling out of the signal or lamp thus giving a white light or a false clear. Many lives were lost due to this exact occurrence on railroads over many years. The worst of such disasters happened on the P.R.R. in 1915 when a cracked red roundel fell out of it's semaphore spectacle giving that fatal false clear indication. A high speed passenger train collided with the rear of a stopped train on the mainline as a result.

The obstacle to the standardization of signal colors was in the providing of a good caution indication. The British had early on (in the 1870's) adopted "red" for stop and "green" for clear thus eliminating the false clear of a broken signal glass. But the problem of distinguishing between a "home" semaphore signal and a "distant" had yet to be successfully addressed. Further, the shades of greens extant varied from a yellow green to a blue green, and the yellows from a yellowish orange easily confused with red to a yellowish green; thus many "yellows" were easily confused with "green". The Railway Signal Club (forerunner of the RSA and later AAR) had for several months entertained the use of a "violet" for the caution aspect in the mid 1890's but quickly reversed that decision to the red, green and white since the violet indication was found to be too short range for mainline use.

The Nels "Baird Yellow Roundel" of the late 1890's was adopted as the intermediate or caution night signaling aspect first by the New Haven in 1899. The Railway Signal Club physically met at Boston's South Station to witness the effectiveness of the new colors and made motion for the adoption of this new "yellow" as the standard caution night aspect.

Enter Dr. William Churchill of Cornell University who immediately after the turn of the Century went to work on establishing the parameters of color characteristics and light and dark limits for all signal standard glass at Corning Glass Works in the Southern Tier of New York State. His work resulted in six RSA standard colors and was accepted and signed into officialdom by the R.S.A. on October 10 1905 . This date is found as a legend molded onto the rims of many early period lenses and roundels.

The standard colors were (and still are) RSA Signal: Red, Yellow, Green, Blue, Purple and "Lunar White." Lunar White is a pale blue glass that, when lit, appears as pure white, just like the light from a full moon or the walk sign found on a corner traffic light. In time, these color standards were adopted by the U.S. Federal Bureau of Standards, not just for railroads' signal light colors, but for navigation, automobile (highway) and aviation signal lights. They eventually became the world-wide standard for all transportation day and night signal colors. Click here to see a scan of the original RSA specifications.

Fast-forward to the present. Nowhere, before or since that 1905 event, has the term "cobalt blue" been officially used for any signal glass color. However, that color term has been used in modern times to describe four of the six RSA colors when signal glassware items are viewed under ambient light. The two exceptions to all such things being "cobalt blue", are red and yellow. Many antique sellers and collectors -- including internet sellers -- use the term "cobalt blue" to describe glass roundels, globes and lenses that, properly illuminated, produce a myriad of hues from middle chrome greens through Robin's Egg blues all the way to deep violets.

This should no longer be simply overlooked or deliberately ignored. By going back to the original terminology -- the RSA specifications -- collectors will not only achieve greater accuracy in their descriptions but will also better preserve the historical record. After all, a major reason for collecting is to keep railroad history alive, and that includes the original terms used in the industry. The use of inaccurate color descriptions works against that purpose.

Shown below are photos of different railroad glass colors to illustrate this issue. Click on any image for a larger version.

Right. Here are lenses illustrating the official RSA Colors: Top - RSA Red, Yellow, and Green
Bottom - RSA Purple, Blue and Lunar White
Right. Here are the opposite sides of the three bottom lenses shown above, from left to right: RSA Purple, Blue and Lunar White
Right. These three lamp's lenses, all so-called 'cobalt blue', are the very same lenses depicted above and in the same order. But they are lit and thus have very different appearances. Obviously using the term 'cobalt' for all three entails the risk of serious confusion.
Right. An RSA green lens is shown on the left, and an RSA blue lens is shown on the right.


Comments? Send email to: webmaster@railroadiana.org



Sent November, 2016: "In retort to your article on RSA lens colors, it is certainly nice to see such descriptive historical information in an article. So descriptive and specific I would have thought it would contain proper footnoting of sources so that interested individuals as myself could view the original source of the material. It would be nice if you could kindly contact the author or alert him to this response so these oversights can be corrected. I don't think there is a better place than Railroadiana.org to harbor such detailed historical information. But as far as terminology in use in the hobby versus manufacturing and railroad standards, I find this level of scrutiny knitpickish, unnecessary and a fair bit obsessive-compulsive. Even the author himself uses alternate "non-RSA" terminology to describe in his own words "glass roundels, globes and lenses that, properly illuminated, produce a myriad of hues from middle chrome greens through Robin's Egg blues all the way to deep violets.

Thanks for keeping up this great website and serving us fellow collectors!" [Scott N.]

Sent April, 2017: "SCOTT N., Your saying "nitpikish" doesn't direct me as to the source of your actual complaint. I then take it you were offended by my stating any use of the term "cobalt" to describe railroad signal glassware is unquestionably incorrect? You haven't been entirely clear with your complaint.

As described and illustrated in the above article, "cobalt" is useless as a descriptive when applied to railroad signal glassware. Railroad Signal Association (R.S.A.) Signal Blue, Signal Purple and Signal Lunar White are all shades of what is euphemistically referred to as "cobalt-blue" glass, but the R.S.A. colors when lit, are without question, most distinctly different.

Your personal slighting of me (with your O.C.D. reference) makes me believe "Psychological Projection" is involved here and it seems I've hit a nerve. Are you "guilty as charged" of erroneous referencing of railroad signal glass perhaps?

I'd suggest you get yourself a copy of the 1911 signal Dictionary (Simmons-Boardman, New York 1911) usually available for under ten bucks on CD ROM, often on eBay. I'd also recommend you read all of it (it is a tome!) and please attempt to find any reference to "cobalt" being used as a descriptive for railroad signal glassware. On page 384 (figures 2675-2679)are presented the precise and official R.S.A.'s names for the 6 standard signal glass colors and note: "cobalt" is no where to be found.

You might also try to find for yourself a copy of the A.A.R.'s "History & Development of Railway Signals" (A.A.R., Chicago, 1953) and read about the history of the development of railroad signal glass by Dr. William Churchill of Cornell University while at Corning Glass Works circa 1905. Again, you will not find a single reference to the term "cobalt" when applied to railroad signal glassware as well as any of the other jargon derived names of signals glass colors such as: amber, teal and cranberry. All of which are of course non-railroad terms and unfortunately remain popular with many hand lantern collectors. Specifically, "teal" was a British antique trade term for any greenish-blue glass and was first used in 1927.

Any footnoting by myself would be pointless as in all probability, you wouldn't be able to find copies of many of the works I used. The last time I used footnotes was in my Graduate Thesis. Unless professional caliber scrutinization is necessary and anticipated, it is a great deal of (unnecessary) work. The additional bibliographical material listed below will have to suffice:

"Railway Signaling", 1921, E.K. King, McGraw-Hill Book Company, Inc., New York
"The Block System of Signaling on American Railroads" 1901, B.B. Adams Railroad Gazette New York
"Automatic Block Signals and Signal Circuits" 1908, R. Scott, McGraw Publishing Co. New York
"American Practice in Block Signaling" 1891, The Railroad Gazette, New York
"The Signal Dictionary" 1908, Simmons-Boardman, New York

As well as various signal catalog dating back to the 1880's from:

The Johnson Signal Company,
The Hall Switch & Signal Company,
The Union Switch & Signal Company, and
The General Railway Signal Company

As well as the series of publications on the complete subject of railroad signals from the A.R.A., --The American Railroad Association (post 1937 known as the A.A.R., Association of American Railroads) and
The periodical "The Signal Engineer" (later "Railway Signaling") Simmons Boardman Publishing Co. 1908-1932.

Many of the sources above date back to as long ago as the 1880's and one or two publications were originally formerly from the Franklin Institute's technical library as they were deemed of "insufficient significance and obsolete" at around 100 or so years of age. You may be able to find a copy of the Union Switch and Signal 1894 catalog (one was recently offered on eBay) and learn the colors of signal glass with in it were limited to "red, green and white" specifically being mentioned ...no other color(s) being referenced by any specific name.

Further, I do sincerely doubt you've ever actually researched this subject on your own and that you're simply repeating what too many others have incorrectly told you. I'm quite certain that had you done a bit of your own research, you'd fully agree with me.

Kind Regards,