“A room with a quarter of a million images”: home labour and microscopy

Lea Beiermann, PhD candidate at FASoS, works in the History Department and is a member of the MUSTS research group. Her NWO-funded PhD project looks at the history of microscopy in the mid-nineteenth century. In her blog, Lea deals with how microscope-using scientists started to share and preserve their slides during the mid-nineteenth century, and the kind of work that went into that.

Have you ever used a microscope? You probably have – at school during biology class, or you may have caught spiders with a “bug viewer”, a simple magnifying glass mounted on a plastic cup. You may have counted the spots on a ladybird’s back, or observed microscopic plants and animals in a drop of water. No matter what you observed, you probably set the bugs free and discarded the water sample later.

Scientists, however, often need to fixate the plant or animal on a microscope slide, so they can keep it, pass it on to other scientists, or compare the specimen on the slide with others. To do so, scientists rely on permanent slides, which help to preserve the specimen for a long time. Making permanent slides requires elaborate preparation techniques: specimens are cut into razor-thin sections, often cleaned and stained, then mounted in Canada balsam or some other mounting medium, and finally sealed with a cement ring and cover glass.

It was around the mid-nineteenth century that those who worked with microscopes developed very elaborate preparation techniques. At the time, there was a growing demand for museum objects – including microscope slides – and slide making became increasingly professionalized. Slide makers established “microscopical institutes”, microscopy supply businesses, which sent the slides they produced to scientists and scientific institutions all over Europe and the United States. In 1861, Neues Frankfurter Museum reported that one such institute alone, the Swiss manufacturers Engell & Comp. near Bern, had produced “thousands and thousands of the most excellent microscopic objects”. The slides produced by institutes like Engell & Comp. are still part of museum collections today.

Despite the large number of slides produced by professional slide makers, little is known about their work. Most commercial slide makers were no aspiring scientists, and they are not remembered for great scientific discoveries, yet their steady supply of slides facilitated scientific research. Therefore, studying microscope slide makers allows us to better understand how microscope slides were shaped not only by scientific conventions, but also by the more business-oriented decisions of the craftspeople who supplied scientists and scientific institutions with their products.

The Naturalis Biodiversity Centre in Leiden holds a large collection of slides, as well as letters written and received by the Dutch slide maker Johannes Kinker (1823-1900), which sheds light on the work done by slide makers. Kinker, originally a stockbroker and bookkeeper, was in contact with the most prominent slide manufacturers of his time, such as Johann Diedrich Möller, Eduard Thum, and the chemist Otto Witt in Germany, Frederic Kitton in England, and Jean Tempère in Paris. Many of the slide makers Johannes Kinker corresponded with were, like Kinker himself, diatom arrangers (or diatomists). Diatoms are microalgae with glass-like cell walls. Their ornamental, colourful shapes as well as their wide geographical distribution made diatoms very popular microscopic objects – to the extent that their collectors were sometimes referred to as “diatomaniacs” by microscopists less invested in such research.

Kinker’s letters show that slide making consisted of manual labour requiring skill in the making and mixing of mounting ingredients, a steady hand and good eyesight. Diatoms had to be extracted from a sample of soil or water, and they had to be thoroughly cleaned before they could be mounted. Slide makers designed all sorts of devices to facilitate their work – ranging from mechanical fingers that made it easier to pick up and arrange diatoms, to breathing tubes that used a slide maker’s breath to temporarily fixate diatoms on a slide. These prosthetic devices demonstrate that slide making was bodily work, which even the most committed slide makers regarded as dreary and taxing on their health. Slide makers therefore carefully considered which kinds of slides could be produced profitably. Some of them turned to making more decorative slides that surprised their viewers with colourful diatom arrangements as those were often easier to make than the slides commissioned by scientists.

Despite slide makers’ capacity to produce “thousands and thousands” of slides, as reported by Neues Frankfurter Museum, they tended to have small business premises, often working from within their own homes. Engell & Comp. was a one-room workshop in a “nice and simple [einfach schönen] house”, while the well-known German slide maker Johann Diedrich Möller made slides in his study. In keeping with their domestic surroundings, the two slide making businesses, as well as many others, were family enterprises: the director of Engell & Comp., Conrad von Rappard, collaborated with his wife and his sister-in-law, Albertine and Louise Engell, while Möller was assisted by his brothers.

Slide makers thus continued a long tradition of household labour in natural history. Coincidentally, the capacity to produce a large amount of slides in small, domestic places mirrored a widespread rhetoric of microscopes revealing a “world of wonders” in even the smallest, most common objects. Neues Frankfurter Museum delightfully called Engell & Comp.’s workshop a “room of a quarter of a million images”.

Today, little-known sources like Kinker’s letters in Leiden make it possible for us to step into slide makers’ workshops again. From Kinker’s letters, we learn that the preparation techniques developed by Kinker and other slide manufacturers made some specimen features more visible than others, and that slide makers’ economic considerations had an impact on the kinds of slides they produced and circulated. Ultimately, we can begin to acknowledge the labour that went into making those “quarter of a million images” and understand how it shaped what researchers saw (and still see) through the microscope.