Hi Everyone. I thought I'd share a few photos of lamp projects I am working on... I am restoring examples of both GE and Westinghouse magnetite arc street lamps to operational condition. Apparently there are very few examples of these that have survived intact as they were mostly removed from service in the late 1920's and their heyday of use was 1908-1925. It has been an ongoing project for some time trying to get them working. I find myself often fabricating missing parts and hunting down obscure historic factory literature in order to correctly repair them. There are quite a few of the GE version of these called the "Luminous Arc Lamp" that have been converted to incandescent bulb fixtures that one sees in collections but it is nearly impossible to find these lamps with their electrical and mechanical inner workings intact. Because these were only used as outdoor street lamps by large utility's very few survived the depression era scrap pile.
 This technology was invented by GE's famous inventor and engineer Charles P.Stinmetz in the 1900-1904 era. Only a few larger manufacturers made these lamps. GE and Westinghouse in the US and Siemins in Europe. Each manufacturer had their own version designed to get around the other manufacturers patents.
   These lamps use an arc electrode made of copper in conjunction with an electrode made of magnetite, titanium dioxide, and chromite oxides. Because these lamps produce a sooty brown powder during operation they were not suitable for indoor use. The lamps all have a vent chimney in the center to remove exhaust gasses and soot produced by the lamp's arc. These lamps purportedly had a much better quality of light then the carbon arc lamps that proceeded them, a light that approached natural daylight.
It will be interesting to see one finally work and see what the light looks like as no color photos or videos currently exist of these once ubiquitous lamps in operation. At one time there were over 300,000 of the General Electric magnetite lamps in service in many major cities in North America along with much smaller numbers of Westinghouse lamps.  I do not know how well adopted these were across the pond or if any Siemins lamps of this type have survived in private collections of museums. 
 Both of the lamps shown here were designed to operate on 4 amp DC constant current series circuits and require a DC current regulator to operate. The GE lamps use about 310 watts and the Westinghouse lamp consumes about 280 watts with 67 Volts across the arc on each unit.
   

Oh my! I finally get to see an actual metallic flame arc lamp, instead of a catalog illustration!

For the record, ten years ago or so, I was highly interested by arc lamps, so I extensively read some of the catalogs listing arc lamps LOL.

The colour of those metallic flame arc lamps was described as bluish-white, resembling daylight. Though referring to it as "better quality" is probably stretching it a bit, as plain carbon arcs already have a nearly complete light spectrum, so it can hardly get any better LOL.

What is the difference between magnetite arc lamps and carbon arc lamps?

The original arc lamps (especially the enclosed arc lamps from after 1895-1900) used electrodes usually made of a combination of lamp black and tar, and were often referred to as "Columbia carbons". In the later years of arc lighting different materials were used as a replacement of the original electrodes. Magnetite was one of them, and such electrodes would burn for much longer. As previously mentioned, special electrodes were also developed using various metals, and arc lamps using those electrodes were called "metallic flame" arc lamps, as opposed to the "carbon flame" arc lamps.