Remaking a local object: The Kirschmann coaxial colour mixer

Over the past couple of months, I’ve been building a 3d-printed model of a nineteenth-century psychological instrument used to demonstrate the nature of colour perception. The model, and, to a certain extent, the effects that it creates, can be seen in this video, though the actual blending effect is smoother and more coherent than the camera is able to show:

The project is partly a way to explore Toronto’s place within the early history of psychology. The instrument, sold beginning around the turn of the twentieth century by the Zimmermann workshop in Leipzig Germany as Farbenmisch-Apparat nach Kirschmann (“Colour mixing apparatus after Kirschmann’s design”), was devised, in part at least, by August Kirschmann (1860-1932) a German-born scientist who led the recently founded Psychological Laboratory at the University of Toronto from 1893 to 1908.

Kirschmann’s apparatus (left) as it appears in the 1893 Zimmermann catalogue of psychological apparatus. The illustration shows only part of the apparatus which I’ve taken to calling the “masking wheels”. Its description says that the apparatus resembles item 12, the “Rotations-Apparat mit Doppelachsen”, a coaxial disk spinner shown on the right. Digitized images are from the digitized catalogues of the Max Planck Virtual Library.

Kirschmann’s apparatus (left) as it appears in the 1893 Zimmermann catalogue of psychological apparatus. The illustration shows only part of the apparatus which I’ve taken to calling the “masking wheels”. Its description says that the apparatus resembles item 12, the “Rotations-Apparat mit Doppelachsen”, a coaxial disk spinner shown on the right. Images are from the digitized catalogues of the Max Planck Virtual Library.

The original instrument, which appears to incorporate two nested axles, would require a machinist’s skills and tools to reproduce. The model is made from various 3d-printed parts, copper gas pipe (easily cut to length with a 10$ pipe cutter), skateboard bearings, and various common nuts and bolts. It is meant to be very easy to make. It isn’t meant to replicate the appearance of the original instrument but rather to function in a similar way.

Exploded View

An exploded view of the model. 3d-printed parts are indicated in blue. Using a combination of 3d-printed fittings and other parts seems to make good use of current consumer level FDM printers.

Colour at the turn of the twentieth century

Over the late nineteenth and early twentieth centuries, the practice of experimental psychology was taking hold in laboratories across Europe and North America. The sensory physiology of colour perception was an important area of research. Sight is a particularly important channel for gathering information about the world. Various forms of colour blindness, for instance, provided clues towards understanding the physiology of sight as well as an important example of the varieties of individual sense perception. For some, experimental psychology also promised a new avenue from which to approach philosophical questions about beauty and aesthetic pleasure.

August Kirschmann

A photograph of Kirschmann taken while he taught at the University of Toronto. Image provided by UTARMS.

August Kirschmann did his graduate studies in the Leipzig laboratory of Wilhelm Wundt (1832-1920). Wundt is generally considered the founder of experimental psychology as a discipline distinct from philosophy on the one hand and physiology on the other. Kirschmann’s thesis, completed in 1891, explored visual phenomena such as brightness and colour contrast. In 1893, Kirschmann came to Toronto to serve as a laboratory assistant in the recently-established Psychological Laboratory at the University of  Toronto. The Laboratory’s American founder, James Mark Baldwin (1861-1934, also a former student of Wundt)  had departed that year for a more prestigious position at Princeton University. Kirschmann, who at first knew little English, found himself in charge of the new laboratory. Over the next decade and a half, numerous students at the laboratory took up Kirschmann’s investigations into colour.

A material culture of colour

The practice of experimental psychology depended heavily on the development of specialized instrumentation. While working as an assistant in Wundt’s Laboratory, for instance, Kirschmann co-authored a paper on the control hammer, an instrument used to calibrate the Hipp Chronoscope, an important tool for precision timing.  His graduate research produced at least two technologies: a means to produce near monochromatic light using coloured filters, and a simple photometer. Both were elaborated during his period in Toronto and were adopted by other experimenters.

He also, over the course of his career, created several instruments that were put into commercial production by the Zimmermann workshop in Leipzig. The colour mixing apparatus, which he developed during his time in Toronto, was one of these. From this perspective, the instrument can be seen to represent a process through which the newly-established laboratories in North America began to contribute to the material culture of experimental psychology.

When scientists began performing quantified experiments on the nature of colour perception in the nineteenth century, they faced the challenge of how to standardize colour and lighting in such a way as to produce results that were credible and reproducible. Among the most common of the instruments used to study and teach about colour vision was the spinning disk, of which the colour mixing apparatus is one, somewhat elaborate, example.

The value of these instruments was straightforward: Physically mixing artist’s pigments to produce a given colour is a cumbersome process. Mixing spectral colours—that is colours obtained through the diffraction of white light—requires complicated equipment that is (or at least was) impractical to use in an experimental setting. If, on the other hand, two or more shades are painted on sectors of a disk, and the disk is spun with sufficient speed, the shades will appear to blend into an even mix of the constituent colours—one example of the flicker-fusion phenomena.

Spinning disks, in various forms, represent a key part of the material culture of early experimental psychology and are well represented in the early catalogues of scientific instruments. Elsewhere, I’ve discussed the variable colour mixer, an instrument which allowed experimenters to vary a blend of colour on a spinning wheel in precise increments—the U of T psychological collection contains several of this type most of which were built locally. With such an instrument, an experimenter could, for instance, probe the threshold of the eyes sensitivity to colours of different wavelengths under different lighting conditions—a phenomenon known as the Purkinje effect.

Variable Mixer

Two variable colour mixers. The instrument on the left is a precision experimental instrument made by the Zimmermann workshop in Leipzig, Germany most likely in the first decade of the 20th century. The second instrument was likely made in a workshop at the University of Toronto.

Whereas the variable mixer was, by design, an experimental instrument, Kirschmann’s coaxial mixer was a didactic instrument  meant to demonstrate the constituent colours of white light as well as various phenomena that occur when mixing colours on a spinning disk. Like other instruments from the period, for instance mineral tubes which fluoresce when a current is applied, it is meant both to demonstrate a scientific phenomenon and to provoke an aesthetic reaction by showing “surprising phenomena” (überraschende Erscheinungen). 

Remaking an instrument

A basic colour wheel is a simple machine. Art students studying colour theory are still assigned experiments that involve spinning coloured disks on electric screwdrivers or kitchen mixers. Kirschmann’s coaxial apparatus is slightly more complicated since it involves two disks spinning at different rates. The “masking wheel” spins in front of the “colour disk”, hiding a certain portion of the coloured wheel and establishing a mix of colour. The slight difference in the rate of rotation means that the portion of the colour disk viewed through the holes on the masking wheel changes from moment to moment. This creates a colour changing effect that depends on the type of masking wheel—the Zimmermann catalogue shows six different wheels, I have so far recreated five of these.

The main challenge in building the model was a lack of information . When I started the project, my only source of information was a very general description of the instrument found in the digitized Zimmermann catalogues of the Max Planck Virtual Library. These also provide the  black and white illustrations shown in the second image of this post. No historian that I had spoken to at that point had seen one of these coaxial mixer.

Based on this information, I more or less understood how the instrument worked and set about drawing up the 3d printed fittings using the SketchUp software—an easy-to-use 3d modelling program whose basic version is free. Midway through this process, I had some very good luck. Looking around a Department of Psychology storage room I happened to open an unmarked wooden box and discovered (or rather rediscovered since members of the earlier UTMuSi cataloging project were aware of it) a version of the coaxial colour mixer. I have since catalogued it.

UTSIC Kirschmann Apparatus

Instrument 2015.psy.160 in the UTSIC collection, the Kirschmann Coaxial Colour Wheel. Note that the disk showing simultaneous complimentary colours has been recreated in a different, perhaps improved, format. The model provides an opportunity to study the difference between these two disks.

At first I somewhat carelessly imagined this instrument to be a prototype or a specially-made version of the instrument shown in the 1893 catalogue. Later, as I went through the digitized catalogues in the Virtual Museum in more detail, I discovered that this was a later version—a model made in the form of a lantern slide which was meant to be placed in front of a slide projector to be shown to a classroom of students. This instrument appears in the 1912 Zimmermann catalogue. It will take substantially more research to determine precisely when these instruments appeared since the collection of digitized Zimmermann catalogues in the Max Planck virtual library is incomplete.

Kirschmann Apparatus for Projection

The version of the Kirschmann coaxial colour mixer used with a projector. This image is from the digitized catalogues of the Max Planck Virtual Library.

This object in the UTSIC collection provided a wealth of information such as pulley ratios and the precise shape of the mask disks. It also showed the colours involved and their arrangement though this is something of a guess since the pigments may have faded unpredictably with time and since the original colour wheel was shattered. It allowed me to make a first model of the instrument which shows some version of the effect. I won’t digress on the building and design process here. If there’s any interest in recreating it, I can post some detailed instructions along with various templates and the .stl files for the 3d-printed parts.

If I’ve taken something useful from this project, it’s a sensitivity to the material culture of colour as it existed at the turn of the twentieth century and as it exists now. This is a period in which calibrated colour sets were only just becoming commercially available and international standards for colour and illumination had not yet been established. Much of Kirschmann’s research involved advancing the development of accurate colours. I’m slowly putting together a journal article on the subject.

The creation of this model highlights the vast technological development that has taken place in this area.  The transparent coloured disc used in the Department of Psychology’s instrument would have been extremely tedious to produce, with each tiny sector cut separately from gelatin sheet and pasted into place with no gaps or overlap.   Recreating it was simply a matter of sampling a digital photograph and adjusting the colours to be as saturated as possible. After that, I laid out the coloured sectors in a drawing program and then laser printed the image onto transparency sheet. Several layers of colour-printed transparency sheets glued to a disk of thin acrylic  (cut from a sheet with a Dremel tool) places a good amount of pigment in the path of the transmitted light—possibly more than was available on the original instrument, though it’s hard to tell since the original gelatin sheet seems to have faded over the past hundred years.

The technologies involved in this recreation process, from the CCD in the digital camera, which captures an accurate impression of reflected light as the human eye would perceive it, to the laser printer, capable of representing a vast range of colour though the process of additive-averaging colour mixing, demonstrate our society’s mastery of colour technology—a process of development whose early origins are, to a certain extent, embodied within this historical instrument.

Aesthetic opinions

As a demonstration instrument, Kirschmann’s colour mixing apparatus is, in certain respects, an aesthetic object. As such, it recalls (maybe a little obliquely) Kirschmann’s curious efforts to reground the philosophical discipline of aesthetics in a rigorously scientific study of human perception. Kirschmann had strong opinions on the subject. In a polemical passage on the subject in a paper published around the turn of the century entitled “Conceptions and Laws in Aesthetics”, he claimed that:

All expressions used in aesthetic and art-criticism which can not, unambiguously and without contradiction, be defined in terms of really simple elements…. are nothing but pseudo conceptions; and all distinctions and classifications into which such expressions enter are illegitimate or pseudo-distinctions; and all alleged knowledge based on such conceptions and distinctions is sham-knowledge; and if the originators and propagators adhere to such expressions after they have realized the truth of what is said above, it is not only sham-knowledge, it is then imposition, deception, fraud.

Experimental psychology was to provide these “simple elements”—basic truths about human perception upon which aesthetic judgments were to be grounded and through which opinions were to be articulated with scientific clarity. This program is apparent in the research carried out at the Psychological laboratory at the University of Toronto. For instance, one of Kirschmann’s graduate students, Emma S. Baker, conducted experiments on colour combinations in order to determine the laws underlying aesthetically pleasing contrast.

Kirschmann’s own aesthetic opinions were conservative. He promoted a kind of visual literalism with regards to the depiction of light—a principle, he believed, that the great painters of the past had maintained implicitly. He wrote that:

By cleverly making use of [the law of contrast, the painter] may even raise the intensities of very small, white, yellow, or orange surfaces so as to give the appearance of a certain luminosity, as for instance, in the case of glowing coals and sparks of a smith’s fire, the illuminated windows in an evening landscape, the Alpine glow, etc. But he should never try to paint the flames of candles, lamps, or torches themselves, or the celestial bodies, for this is, with respect to true reproduction of intensities, absolutely impossible.

Kirschmann appreciated Rembrandt’s “somber brown tone” because “the yellow and orange side of the colour manifoldness (brown is always a shade of yellow or orange) admits of the greatest number of intervals between full saturation and the darkest shade.” The impressionist movement, by contrast, sacrificed

all truths of intensity for a certain mannerism in colours. They paint everything in a kind of purplish gray haze, and they call that impressionism, although such impressions can only be obtained by seeing things in a veiled mirror or through a cloud of cigarette-smoke.


“Claude Monet, Impression, soleil levant” by Claude Monet – Licensed under Public Domain via Wikimedia Commons –,_Impression,_soleil_levant.jpg#/media/File:Claude_Monet,_Impression,_soleil_levant.jpg

Kirschmann was, like many scientists of his day, something of a polymath. He wrote on subjects ranging from logic, to mathematics, to public education—he was a great promoter of the research model embraced by the German universities believing that North American universities should follow that model rather than emphasizing general education.  His forays into aesthetics may be partly explained by the fact that he was a professor of philosophy—the nascent practice of experimental psychology took root in Toronto within the existing Department of Philosophy, as it did elsewhere in Europe and North America.

As with other scientific objects, Kirschmann’s curious demonstration instrument provides a kind of window into the past opening onto a variety of historical themes. It takes us into a period in which practices, developed in the German research system, were being absorbed in North America along with their material accouterments. The study of colour perception was a key area of interest for experimental psychologists. The collection of psychological material at the University of Toronto ought to be considered a key material archive for studying this area. The process of recreating such instruments also deserves consideration as a scholarly research technique.


I am very grateful to Gabby Resch and Isaac Record of Semaphore Maker Labs for help on various 3d printing projects as well as to David Pantalony and Christopher Green for their advice on the history of psychology. 

I would also like to thank Michael Spears and Erica Lenton at MADlab at the Gerstein Science Library. U of T students and faculty can use the 3d printers at MADlab for a very reasonable price after taking a simple safety course.

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