How long is one minute? There is the objective answer of sixty seconds, but there is also the subjective personal perception. One minute can feel like a blink of an eye, but it can also last an eternity. When working in the lab, I often experience both perceptions within a workday. The days are always too short, and I regularly wish that I could live in the lab to work into the evenings. However, during each experiment, time often seems to have stopped moving. One experiment can appear to take forever, and I constantly have to prolong the allotted time for the tests. The temporal aspect of making is amplified, and patience is much required to conduct this slow research.
Taking time to manipulate a material is imperative to observe how matter changes its behavior gradually. The quality of the product usually relates to the time spent on the process as well. Almost every experiment I have done on grinding pigments from various natural sources circle back to the issue of time, when the tools I use to grind them remain consistent. Minerals, such as lapis lazuli, take much longer to grind to fine particles due to their hardness, whereas earth pigments like ochres are less time-consuming because they are generally softer. These observations do not come as a surprise, but going through the motion of grinding makes experiencing time much more intense than reading about it in historical recipes. A recent experiment might be able to visibly demonstrate what time does to change a material.
It is known that over-grinding of certain minerals can result in the pigments losing their brilliance and turning the colors dull. However, how long it takes for a pigment to pass the threshold and become over-ground can vary drastically depending on the type of the mineral and the quantity of the pigment. I wanted to see how easy it is to over-grind malachite using the simple technology of a glass muller and a granite slab. To do so, I put on a batch of malachite powder and ground it with water for ninety minutes. The powder was prepared from a previous experiment, in which I simply broke the stone into small pieces, crushed the pieces into coarse powder, ground the powder with the muller and slab until it no longer produced a cracking and scratching sound, and removed impurities through levigation. I took a little pigment out of the batch every ten minutes to see how the sizes of the particles changed during this ninety-minute process.
Time-lapse is a fascinating film technique which condenses a long sequence into a short period of time. The video (Fig. 1/Vid. 1) of me grinding malachite gives a deceptively brisk working pace that appears to be full of energy and excitement. In reality, the process was agonizingly long and taxing. Ten minutes into grinding, I was already losing my patience. The ten-minute marks never arrived fast enough, and there were still so many ten minutes to go. When grinding, there was no highly noticeable visual and tactile difference in the texture of the powder-water mixture. It was smooth and easy to be pushed around. However, the color of the mixture gradually became ever-so-slightly paler in the first half hour of grinding, and it was most observable when placing a small sample of the mixture onto the plate at the end of each ten-minute mark (Fig. 2). The color of the mixture stopped changing around the forty-minute mark, but I continued to complete the full ninety minutes of grinding.
Fig. 1/Vid. 1. Time-lapse of the malachite grinding experiment (or link to Youtube).
Fig. 2. Samples of pigment ground for different lengths of time.
I left the pigment samples on the plate to dry and called it a day in the lab. Two days later, I returned to the samples and bound them with gum water to turn them into watercolor paint. Each sample became a small swatch painted over a strip of black India ink to test its opacity (Fig. 3). Immediately, the powder that did not undergo further grinding (0 minute) shows that the particles are too coarse to make a good paint. The sample with ten minutes of grinding time shows an improvement in the paint quality, but still not good. The swatches painted with pigments ground for thirty minutes or longer are more similar, in their colors and the smoothness of the paint surfaces.
Fig. 3. Swatches painted with watercolor paints made from pigment samples ground for different lengths of time.
Despite the change in color to a paler green, I do not think that I have over-ground the malachite. The darker greens have appealing colors, but the paints did not behave well. The higher grinding time resulted in finer particles, but more grinding did not further alter the color of the pigments in a highly visible manner. Rather, pigments with higher grinding time can be more evenly mixed with gum water to make paints with a better flow. Time, in this experiment, is a critical element to produce usable pigments, and it needs to be accompanied by the patience of repeating the same motion for a minimum of thirty minutes.