Dr. Colin G. Fink

Colin Fink was born in Hoboken, New Jersey on 31 December 1881. He earned a Bachelor of Arts degree from Columbia University in 1903. He then earned both a Master of Arts degree as well as the Ph. D. degree from the University of Leipzig in 1907 (summa cum laude).

When Fink returned to the United States he entered the Research Laboratory of the General Electric Company in Schenectady, New York. It was here that he developed "Dumet", a two-component metallic wire which for over a century, has remained the preferred material for the formation of glass-to-metal seals used in electric lamps and other glass electrical devices.

Fink's career after his stay with General Electric was continued in academia. He was professor emeritus of chemical engineering at Columbia University and head of its division of electrochemistry from 1922 to 1950. Quoting from the New York Times³:

"Perhaps he became best known among non-chemists for developing electro-chemical methods to restore old bronze and for detecting art frauds. It was through his process of 'turning rust back to metal' that the Metropolitan Museum of Art was able to restore priceless Egyptian antiques in bronze.

"...His discovery of a process for coating steel with aluminum once had been regarded as impossible. He forecast in 1937 that this new form of steel, resistant to corrosion and yet possessing the great tensile strength of steel, would have far reaching effects in airplane and auto design, rail equipment and industrial machinery. He lived to see much of his prediction come true."

The common leading-in wire in incandescent lamps today consists of "Dumet" in the seal region. Dumet was a development of Colin Garfield Fink in 1912. He was issued U.S. Patent 1,498,908 on 24 Jun 1924. So - what is it that Fink did that resulted in a leading-in wire that is still used today? This is perhaps best told by quoting from Fink's patent. He said:

"In order to make a seal...which will be gas-tight, the leading-in conductor used should preferably have a coefficient of expansion which does not differ greatly from that of the material of the envelope. It is also necessary that there shall be a certain affinity between the material of the envelope, when in a plastic or partially liquid condition, and the surface of the conductor, by reason of which there will be a tendency for the two to stick together. This property is usually spoken of as a "wetting" of the conductor by the material of the envelope. When the envelope consists of ordinary glass, platinum has been found especially suitable for a leading-in conductor because of the fact that it is practically non-oxidizable and has a coefficient of expansion which is nearer to that of the glass than any other metal, and also because platinum is "wet" by glass. Because of the great cost of platinum, however, many efforts have been made to secure a suitable substitute. It has been found that if nickel and iron are alloyed in the proper proportions, a conductor may be obtained which has the same coefficient of expansion as glass. In attempting to use such a conductor in commercial practice, however, difficulty has been experienced because of the large number of seals which are defective. This is probably due to the fact that when subjected to the heat of the flame necessary for the sealing-in operation an oxide coating is formed which is more or less porous and allows air to gradually leak through between the glass and conductor. It has also been found difficult to prevent the formation of bubbles in the seal due to the liberation of gas from the conductor or the formation of gas by chemical reaction during the sealing-in operation.

"I have discovered, however, that there are certain metals whose oxides are readily soluble in glass at lamp seal making temperatures. Among these are copper and cobalt and some of their alloys. Ordinary lead glass, such as commonly used for incandescent lamps and rectifiers, has a coefficient of expansion of about 8.8x10^(-6) while copper and cobalt have coefficients of expansion of about 17x10^(-6) respectively. Hence, solid conductors composed entirely of either of these metals are not commercially suitable for leading-in conductors because of the great difference between their coefficients of expansion and that of glass. By making a composite conductor, however, having a sheath of copper or cobalt and a core of metal having a lower coefficient of expansion than that of glass, and by properly proportioning the relative thicknesses of the core and sheath, it is possible to provide a conductor, the total radial coefficient of expansion of which is substantially the same as glass with which it is to be used. I have found that if such a conductor is used that there is an even better union in the cold state between the conductor and the glass than in the case of platinum. In actual practice it has been found that by using my invention the number of defective seals has been reduced over 75% from the number commonly found when platinum is employed."