Joined: 09 Jun 2009
Location: Bromley, Kent, UK
|Posted: Thu Jan 25, 2018 7:54 am Post subject: Crystals of some common and easy to get chemicals II
|My enthusiastic 10 year old neighbour and I recently made some more crystal slides. Easiest and perhaps most interesting was stearic acid. Stearic acid is a saturated fatty acid with an 18-carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid and its chemical formula is C17H35CO2H. Its name comes from the Greek word ????? "stéar", which means tallow.
Stearic acid melts readily at low temperature (69 degrees C) and produces interesting and unusual waxy crystals when it cools. It's readily available on eBay, as its used in home made candles, soap and cosmetics and is very non toxic. The crystals produced work well with ordinary pol +/- a retarder as well as DIC +/- a retarder. Attractive pastel colours and unusual shapes are produced, which make a nice change from the more garish colours produced by many crystals with polarised light.
To produce crystals we simply placed a few milligrams of solid stearic acid on a clean slide, melted the solid on a warm heating ring, and immediately placed a coverslip on top. Crystallisation occurred immediately on removing from the heat.
Different areas on the slide produced a range of interesting shapes and use of different retarders in conjunction with polarised light and DIC (one of my favourite retarders is two layers of ordinary Sellotape on a clean slide) gave a range of more subtle colours.
Leitz X4 plan fluorite objective, polarised light with retarders.
Leitz X4 plan fluorite objective, polarised light with retarder, stitch of 11 images.
Nikon X10 Plan DIC objective, 'standard' DIC without retarders or variable compensation.
Nikon X10 Plan DIC objective, 'colour DIC' with variable compensation.
Leitz Ortholux 1, Zeiss standard, Nikon Diaphot inverted, Canon photographic gear