growing chrystals

During the first part of Tactile Research Lab, John Sandli began growing crystals, for the specific purpose of making lenses. John: …”My first experiments were with table salt, but soon after I began experimentation with both magnesium sulphate and alum.

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Epsom salt, or magnesium sulphate, when grown from a new hot solution, then rapidly cooled down usually seem form as either a bed of tiny spikes of crystals reaching upwards (img1), or when grown on a larger flat surface as similar spikes, only growing along the surface. While growing them, I’ve noticed a dense, usually almost opaque, base forming at the bottom of the bed. This kind of bed, of tiny crystalline structures is unsuitable for optics. When growing with a large amount of saturated solution, the beds form so tiny crystals, so as to resemble slushed ice. I discovered by pouring some of the remaining, cold, solution of different beds, and reapplying them to other beds grown with very little solution, with only partially formed crystals, that the crystals formed would grow larger, more rectangular in shape rather than spiky (img2). They often formed along the bottom, instead of upwards. I continued pouring off and reapplying solution in this manner, over and over in varying amounts and discovered that the solution-mix would form a thin, nearly translucent base, with larger, unique crystals embedded and fans of crystals growing out here and there (img3).

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I also discovered that by taking some larger spikes as seeds and apply it to such a solution-mix would sometimes form a single larger crystal (imgs4/5). One such turned out to be surprisingly clear with only some faults in the middle going along the crystal. I grew several others, ranging in sizes between two centimetres to up to around four in length. One thing I discovered was how the crystalline structures would enlarge separately while forming a larger crystals. On some crystals you could see it quite clearly, forming a staircase pattern (imgs6/7) along the surface.

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While I’d had some success growing the kind of beds I thought I needed, I’d never been able to get such a result starting from a new solution, only mixed solutions of unknown saturation. To form crystals in any realistic time-frame you will need to cook up a fairly saturated solution, but both the heat and the saturation will affect how the crystals grow, together with how rapidly the solution is allowed to cool down. I tried out different ways of preparing solutions, and found that when dissolved in cold water allowed to slowly heat up on the stove, taking the solution of the heat at between 70 and 80 degrees C, I would fairly consistently (let’s be liberal with the definition of “consistently” here.) achieve either beds with larger spikes or one larger crystal without the need of mixing old solutions. Now, I thought that these beds would be suitable for my purposes, but they turned out not to be, or to be specific, the light-source used was not suitable for these beds. But that’s a different topic.

While growing I noticed oxidation of Epsom salt and alum. After a while when exposed to air, they will get coated in a white layer. This is possible to clean off with water, though when exposed to water Epsom salt will get very fragile. To protect the crystals of oxidation, I tried coating them with various lacquers. My first try was with clear epoxy glue. The glue was difficult to apply because of it’s thick consistency, so I later tried heating the glue first. It was still a bit to thick, so I abandoned epoxy in favour of clear acrylic spray. The spray, when applied liberally, did work to protect the crystals, but in some cases it wouldn’t form a coherent, smooth layer, but rather a layer made up of spots and indentations. This was only a problem in some cases, so I will continue with the spray and see how it works with alum.workspace1workspace2

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I also experimented with magnesium sulphate in another way. Me and Andreas conducted experiments of how a piezoelectric microphone would act in a solution of Epsom salt. We hoped to achieve the sounds of crystals forming. We was able to record such sounds, but we achieved a much more interesting and surprising result: They began behaving as field microphones, picking up air vibrations. The sound was affected by the process of crystallisation, so underneath other sounds you hear blubbering sounds, flutters, pops and clicks of crystalline structures forming. The microphone must be placed on a suitably resonating surface to work. We found wood worked best. We took this with us to Poland where we continued the research and eventually found a use for it in our project. Together with this, we also worked with laser-projections. Lasers appeared to project a microscopic image of the crystals, showing lots of small crystalline structures. The image will have an effect close to that of 3D. Ultimately we projected lasers through magnesium sulphate solutions on a mirror, projecting the crystallisation as it occurred.

While working on growing crystals of magnesium sulphate, I also started experimenting with different plastics. One material I found interesting was dried sheets of wood glue. While cold it behaves semi-rigid, slowly shaping itself back to approximately it’s original shape, but when heated it becomes very soft and malleable. It will to a degree retain the shape given while soft as it hardens again. For each time it is heated, then cooled, it turns more brittle, until it is no longer flexible and breaks. It is also semi-translucent, and will act as a filter when looked through. The closer it is to something, the more it shines through, sort of like baking paper.

I chose not to focus too much on alum during the first semester. They grow a lot more slowly, and they usually form either single crystals or very brittle beds of extremely small crystals. As I was more interested in beds of larger crystals at the moment, I grew alum more as a side project to teach myself more. I did find this very helpful for practice and developing a process. They have a habit of rather forming several larger crystal seeds rather than beds, and can grow quite large when reapplied in solution for continued growth. You have to constantly pour off solution to rinse for competing seeds, the reapply the solution, which helps in developing a method of constant care balanced with as little disturbance as possible. I have now chosen to focus more on alum, as they are a lot easier to grow without impurities, which broadens their use for optical experiments.

I have added a few pictures, labelled as “img[nr]”, but I am notoriously bad at visual documentation, so keep that in mind. I’ve also added some sound file.

– John

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