TUESDAY (17th of September): materials and method
- Potash alum
- Hot water
- Filter paper
- Filter funnel
After making sure that all apparatus is clean and dry, place approximately 25 g of
potash alum in a beaker (250 ml or bigger) and add approximately 170 ml of hot
water. Stir the mixture until all the crystals have dissolved.
(NOTE: don’t use all the alum you have been given – keep a few crystals back in reserve in case you need to “seed” the solution later.)
Filter the warm solution through a filter funnel (in which filter paper has been inserted) into another clean beaker. Cover the beaker of solution with the watch glass or fresh filter paper and set aside in a cool sheltered place and allow it to stand undisturbed overnight. The first beaker and funnel can be washed and dried and the residue and filter paper used for filtration discarded.
WEDNESDAY (18th of September): materials & method
- Crystal solution (from yesterday)
- Clear beaker
- Glass stirring rod (optional)
Observe the solution in the beaker. The bottom should have become covered with a layer of small crystals (these should have formed spontaneously as the solution cooled). Carefully pour off the clear solution above the crystals into a clean beaker and set it aside for later, leaving the crystals behind in the other beaker.
If no crystals have formed overnight, the solution can be “seeded” by adding a crystal from the original alum. Let it stand overnight again and observe the formation of crystals.
Alternatively, if nothing has happened, crystal growth may also be induced by scratching the bottom of the glass beaker with a glass stirring rod.
THURSDAY (19th of September): materials & method
- Plastic spoon, spatula, tongs or tweezers
- Nylon thread (optional)
- Stirring rod or pencil (optional)
From the bed of crystals, one
good symmetrical crystal or group of crystals needs to be selected to act as “seed” for your big crystal. Using a plastic spoon, spatula, tongs or tweezers, transfer the selected crystal to the beaker containing the decanted solution, trying to place it centrally in the beaker.
(A good technique to promote uniform growth is to suspend the crystal with a nylon thread tied round a stirring rod or pencil resting on the rim of the beaker. This step is not essential, however, and good a crystal can usually be obtained just by leaving the crystal on the bottom of the beaker.)
Take a picture of the crystal, preferably close to a ruler so that you can measure its size, and mark the level of the liquid in the beaker. Record the date in your diary. Cover the solution with a loose-fitting paper hat that permits water to evaporate slowly whilst keeping out dust. Allow the solution to stand in a draft free location, not in direct sunlight or near a heater. The aim is to keep the temperature as constant as possible.
HOLIDAYS (23rd of September - 7th of October): materials & method
Once a week record in your diary the level of the solution in the beaker and if possible, without disturbing your crystal, take a picture of it close to a ruler so that you can estimate how much it has grown. Try and avoid disturbing crystals during the growth phase as this may induce additional crystals to grow.
If small isolated crystals appear, you may be able to carefully remove them with tweezers. Be careful not to disturb your big crystal. If small crystals grow on the main crystal, remove it, dry it with tissues, and carefully remove the adhering buds.Do not touch the crystal with your fingers. The crystal is likely to be quite fragile, fairly brittle, and easily damaged, so should not be dropped or bumped.
When it is decided to terminate the experiment (after about 10 weeks or so), remove your crystal very carefully from the beaker, dry it with tissues and with a ruler measure its length, width and height. Compare the measurement, if you can, with the size of the original crystal. Take a photo of the completed crystal (next to a ruler to confirm the size)
To complete the artistic component, students will digitally photograph the completed crystal, and using the effects of light and shade, colour and other techniques, produce an artwork featuring the crystal and demonstrating the principles of diffraction/reflection/dispersion using light and or objects/images (see examples). The ingenuity of students will be encouraged to produce an innovative picture which highlights the crystal.