How to Create Crystal-scapes with a Microscope
Microscope and Set-Up
Microscope photography, technically known as photo microscopy, offers a unique opportunity to view the world from a perspective beyond the realm of the human eye. However, many common microscope subjects, such as insects and biological specimens, do not appear photographically of interest from an artistic or creative point of view. Moreover, these subjects frequently lack one basic element of photographic interest: color.
As many photographers are aware, the success of their work strongly depends on controlling the interaction of light with the subject. Some of the most interesting photographs result from the process of diffraction, where light is separated into its visible components, such as through a prism, or rainbow. Many dramatic abstract photographs are possible using diffraction to separate colors.
Diffraction is not the only mechanism that can separate colors. Interference patterns, which occur in soap bubble films, oil layers films and other surfaces, are often more vibrant than rainbow colors. The interference process, however, does not separate light into the usual orderly array of its component colors (i.e., from red to violet), but rather into a series of colors usually not present in nature. This unusual light separation results in color patterns with strong visual interest. Interference color patterns are also produced when certain chemical compounds interact with polarized light.
Figure 1 shows the microscope needed to conduct the crystal photography. The essential elements of the apparatus are a camera and a polarizing microscope. Any basic SLR or DSLR camera with a removable lens can be used, although I recommend the DSLR to be a better choice. Other equipment includes two circular polarizing filters, a few microscope slides, and some chemicals that change color under polarizing light (to be explained below).
Many microscopes can be easily converted into polarizing models. For SLR cameras, the best to convert for use with polarizers is a trinocular microscope. The camera is mounted to one eyepiece, while the sample is viewed through the other two. For DSLR cameras, a standard (and less expensive) monocular microscope can also be used. Many microscope suppliers of new and used equipment can be found online. Dedicated polarizing microscopes are expensive, probably more than $3,000, but are not needed to obtain stunning photographs. Non-polarizing models, perhaps costing $200-1,000, are simple to modify.
To convert a standard microscope for use with polarizers, some requirements are: (1) the capability for magnifications up to at least 100X, (2) a provision for placing a polarizer above and below the sample, and (3) a mechanical stage for easily viewing the sample at different positions.
A polarizing microscope exposes an optically active material to light that is vibrating in a single direction, followed by viewing the sample at a different angle. This technique, known as cross-polarization, is accomplished with two polarizers: one beneath the sample (the polarizer), and the other above the sample (the analyzer).
In a commercial polarizing microscope, the polarizer is usually fixed and the analyzer is rotated. For a converted microscope the analyzer is fixed and the polarizer is rotated. In both cases, cross-polarization occurs to produce the vibrant color patterns we wish to photograph.
The first step in setting up the equipment is to remove the camera lens and replace it with a T/2 microscope adapter, available at most camera stores, to match the mount on your camera. The microscope eyepiece, or ocular, becomes the new camera lens, which is placed inside the microscope barrel just below the connection with the T/2 adapter. Change the magnification by altering the power of the microscope objective.
The microscope must be used with two circular polarizers (the common filter usually placed over your camera lens), one below and above the sample. For the filter above the sample, use a circle of plastic polarizing material, or a glass-polarizing disk (cut with a diamond or carborundum saw at a glass-blower’s or machinist’s shop) placed in the barrel of the microscope. The second polarizer, a standard uncut camera filter, is placed over the microscope’s illuminating light or the condenser. These are located immediately below the microscope stage. The bottom polarizer is rotated to produce and enhance the color patterns in the sample.
After setting up the microscope, you are ready to add your crystal-producing chemicals.
Chemicals For Producing Colors And Patterns
Many polycrystalline materials rotate the plane of polarized light, which is why they are subjects for photography through a microscope. The intense color patterns produced by viewing these materials under cross-polarization are excellent subjects for creative abstracts, similar to (but more vibrant than) stained-glass windows.
Some useful optically-active materials include copper sulfate, potassium dichromate, ferrous ammonium sulfate, urea, sodium thiosulfate (“hypo”), Borax, and Epsom salts, etc., many of which are obtainable from your drugstore, a commercial chemical supply source, or on the Internet (see chemicals for microscope study).
A wide variety of chemicals you usually have around the house are also optically-active, including vitamin C, vitamin E, the entire vitamin B series, aspirin, and Alka-Seltzer, etc. You can check which ones work before viewing them in the microscope by the method I describe later in this article.
Some chemicals you may wish to study are not soluble in water (the preferred solvent), but perhaps can be dissolved in methanol (rubbing alcohol), ethanol, isopropanol, or acetone, all available from your drug store. Another less convenient process is to melt the crystals on the microscope slide and allow them to cool. A chemical’s insolubility may be caused by the binder used to coat the chemical. To study these materials, you will need to acquire binder-free, pure materials, or employ solvents in which they are soluble.
Why are some materials colored when viewed under cross-polarized light? A beam of polarized light is made up of two components: a right and left hand circularly polarized fraction. No rotation will be observed if these two components are transmitted with equal velocity through a symmetric crystal. For optically active materials, however, the two beams are transmitted at different velocities in different directions because of refractive index variations (due to bonding differences) within the crystal. Upon recombination of the two beams after passage through the crystal, the resulting light beam is out of phase, or interferes with itself, and is separated into specific, vibrant colors. The colors generated are not all of those found in the visible spectrum, i.e. observed through a prism or in a rainbow. The color sequence is known as Newton’s series, and is similar to the interference colors observed in soap bubbles.
In addition to unique colors, the patterns, shapes, and forms you will generate by viewing optically active chemicals under cross-polarized light are also fascinating. Because of the wide variety of geometric forms usually found in one sample, your first impression might be to assume that the material is extremely impure – different patterns result from different contaminants. This is the result of crystallinity differences, rather than impurities.
Crystalline films of this type are called polycrystalline because they exist in different bonding configurations such as cubic, tetrahedral, hexagonal, etc. A material with only one long-range symmetrical bonding possibility is called a single crystal, and does not interact with polarized light.
In optically-active polycrystalline materials under the influence of cross-polarized light, the variety of crystalline forms become visible, usually each form associated with a specific color. The combination of different shapes and colors is what makes this type of photography so exciting.
To prepare the samples for study: (1) Dissolve the material in a small amount of water or another solvent in a test tube or cup, (2) Place a few drops of the solution on a clean microscope slide, (3) Allow the solvent to slowly evaporate to form a thin layer (a film) of crystals on the slide.
The crystal patterns may vary due to the concentrations at which they were prepared and the rate of evaporation. The crystal deposit is often too thick for adequate observation and color formation. Generally, slow evaporation from a dilute solution produces a thin and uniform crystal film.
Another frequent situation is super saturation, in which no crystallization occurs at all. Only a syrupy liquid is produced. A small seed crystal added to the liquid often promotes solids formation, but some experimentation may be necessary.
Different preparation conditions can produce entirely different patterns. Quite often, the crystals formed at the edges of the evaporated pool or in contact with the slide edge are the most dramatic. If new patterns are desired, the dried crystal deposit can be re-dissolved on the slide by adding a few drops of water, stirring the solution, and repeating the evaporation. Thus, one deposit can be photographed many times, providing a seemingly endless array of shapes and color patterns.
It is often not possible to tell in advance which crystal deposits will produce a colored effect under cross-polarization. Some visibly colored materials do not rotate the plane of polarized light, and some uncolored crystals do. A rapid screening technique that avoids the initial microscope and camera set-up is to view a slide containing a crystal deposit on a light box between two polarizers. The observation of color patterns (a loupe may be useful) when one polarizer is rotated will immediately suggest which materials are optically active.
Photographing optically-active materials can yield images with high geometric and color impact, not easily achievable by Photoshop manipulations. Essentially, the microscope converts a shapeless and colorless solid material, illuminated by a tungsten light source, into unique crystal shapes and colors rarely seen outside the microscope.
The final visual success of the crystal image depends, of course, on the same design elements required for any photograph: shape, texture, color, pattern, and form, etc. Fortunately, these elements abound in optically-active crystal photography.
Moreover, you only need one subject, a crystal deposit on a microscope slide, which can be regenerated in countless colors and patterns. The equipment required is usually less than a moderately-priced lens you might purchase for your camera. And finally, you don’t have travel far, wait for good weather, or carry a heavy equipment bag. Subjects wait on your kitchen and bathroom shelves.