Photograph from Kubelka Passport Application Documents, Michal Vik
Paul Kubelka was a Czechoslovakian chemical engineer whose many accomplishments include a theory of light absorption and scattering by a layer of paint. Kubelka was born in 1900 to Austrian parents in Czechoslovakia.
He was educated in the German language, attended elementary school in Kladno and secondary school in Brno and Prague. In 1918, he served half a year in the Austrian Army and began studies at the Technical University in Prague. In 1922, he passed his final examination as a chemical engineer. He then served seven months in the Czechoslovakian Army, where he soon commanded the military analytical laboratory.
After leaving military service, Kubelka collaborated with Werner Mecklenburg, the well-known colloid chemist, at Verein für Chemische und Metallurgische Produktion, in Aussig, Czechoslovakia. During this period, he worked on activated charcoal, resulting in patents and in the gas mask charcoal “G 1000.” One theoretical investigation of this period earned Kubelka a Doctorate of Engineering in 1926. At this time, Kubelka married Margarethe Schönhöfer and they had two children.
In 1928, he led both the Inorganic and Analytic laboratories at his employer company. His laboratory investigated (among other things) high-temperature reactions, the preparation of pigments, and activated charcoal.
In 1931, Kubelka resolved to enter an academic career. Because of his publication on absorption and capillary condensation, he was nominated docent of the University of Prague. There he investigated the absorption of vapors by silica gel, which led to an exact method of measurement of surface tension of crystals. His work interested Fritz Haber and he expected to be nominated as professor at a German University. It was during this year that Kubelka published the famous paper with Munk [1], but he does not mention this in his autobiography.
In 1933, the situation was changed by the Nazi revolution in Germany. Kubelka refused to go to Germany, and had few choices in the rest of Central Europe, so he returned to technological contributions—soon founding the company Kubelka Schuloff & Co., which eventually changed to Dr. P. Kubelka & Co. The company established a research laboratory and later a small factory. Products such as the fungicide Cuprenox were successful. However, World War II disturbed this success and prevented the realization of other inventions. Furthermore, Kubelka was forced to change to German citizenship and then was ostracized by the Nazis. At the end of the war, his German citizenship was nullified, he was promised to regain Czechoslovak citizenship, and he accepted a position as research chemist at the Film Company at Cesky Brod near Prague, branch factory of the Aussig Combine (SPOLCHEMIE). There he worked out a new photomechanical emulsion and reorganized the testing system. Upon deciding to go to America, he was told that the Czech authorities intended to prevent him as a specialist from leaving the country. The only place to emigrate legally was to Germany. Through the date of writing of his autobiography, he then lived in Bavaria with his children, working on the optical theory of light scattering materials and thermodynamics of absorption and capillary condensation. His first wife had passed away during the war and In March 1947, he married Dr. Brigitte Gade.
After immigrating to Brazil in 1950, Paul Kubelka conducted further research to generalize his optical transfer theory to inhomogeneous layers [2, 3]. He passed away on June 23rd, 1954 in Rio de Janeiro, where he was Head of the Research Laboratory at the Brazilian Ministry of Agriculture.
68.1 Kubelka–Munk Theory
This theory, originally published in 1931 with Franz Munk [1], is the basis of much software that performs colorant-recipe prediction (colorant formulation). Whereas the 1931 theory assumed that light flows in one dimension (two fluxes, upward and downward within the layer), and in 1948, Kubelka derived the same equations (up to a factor of 2) assuming spherical scatter within the paint layer [2]. Later, he generalized the theory to inhomogeneous layers [3].
The main contribution of these articles was a closed-form function relating the reflectance R of a layer to two constants characteristic of small particles within the layer: the absorption coefficient K and the scattering coefficient S (both assessed in a unit thickness of the layer). If the layer is opaque, then the reflectance is a function of K/S; otherwise, R depends on K and S separately, as well as on the reflectance of the material behind the layer. The Kubelka–Munk analysis also includes equations for total transmittance of a translucent layer.
Although Kubelka and Munk independently developed their analysis for paint layers, the underlying theory originated with an astronomical motivation, starting with Arthur Schuster’s 1905 paper [4] relating to transmission of light through clouds.
To render Kubelka–Munk analysis useful for colorant formulation, one needed the additivity principle described by Duncan in 1940 [5]. This principle says that the total absorption coefficient K of a layer is the concentration-weighted sum of the K-values of the components (K = c1 K1 + c2 K2 + …) and similarly for S (S = c1 S1 + c2 S2 + …).
Once the Kubelka–Munk theory, the additivity principle, and computer technology had emerged, colorant formulation was on its way. By 1958, Davidson and Hemmendinger introduced the analog Colorant Mixture Computer (COMIC), and this was quickly followed by dedicated digital devices, which in turn yielded to software packages that ran on general-purpose digital computers. The above discussion places Paul Kubelka’s color-science contribution in historical context.