Iron (Fe, Atomic number 26) is my first element in my Periodic Table of photographs. Here represented as steel used in a couple of local bridges.

Fremont Bridge
Aurora Bridge, from Fremont Bridge

Aurora Bridge, in the background, or more correctly called the George Washington Memorial Bridge, carries Highway 99 over the Lake Union Ship Canal.  For an fascinating picture of the last of the tall ships (Monongohela) to get out of Lake Union before its completion in 1932, see the Puget Sound Historical Society’s picture.  Fremont Bridge, halfway through a re-paint, is thought to be the most frequently opening drawbridge in the United States.  Due to its low clearance it opens around 35 times a day.  There is also a counter on the bridge that tracks cycle traffic – and although the annual count hadn’t even lit up the bottom rung of the display, and only 108 bikes recorded on this rainy Sunday – the annual count passed the 1 million figure before the end of December 2014.

Aurora Bridge from the North underside
Aurora Bridge

Iron has also played its part in Photography, and this picture taken under the North side of the Aurora Bridge mimics the cyanotype pictures that used ammonium iron(III) citrate and potassium ferricyanide as the photosensitive material.

In more modern times salts of Iron continued to play a part in photographic chemistry – being used both in early toning process to oxidize a silver image before applying some other tone (using sulphide, selenium or other metals such as gold or platinum), and also used in the more traditional color photographic process in bleach and bleach-fix formulations – where the silver image has performed its task and is removed by oxidation of the silver with Ferric Ammonium EDTA or a similar ferric salt, before the unexposed silver halide is dissolved by the ‘fixing’ agent for later recovery.  In print processing this usually happens in one stage – the bleach-fix.  In color transparency and color negative processing it is common to have two separate stages.

Iron is the 4th most common element in the earth’s crust, and its abundance in rocky planets such as Earth is due to its position as the end point of radioactive fusion chain – being formed when Nickel-56 produced in supernovae decays to Cobalt-56 then Iron-56.  It accounts for over 90% of the processed metal production – the rails and bridges that opened up transportation across land – as well as the ship production and reinforcement in building construction.  Oh, and it also carries oxygen around the body as part of hemoglobin.  Quire useful stuff.

Aurora Bridge from below
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