Dr. Alan Hodgkinson, a world-renowned gemologist, lecturer and author regaled us with a series of slides and techniques that he has developed of the years.
Dr. Hodgkinson began by reminding us that without impurities in stones, there would be no colour! It is the impurities that give us the red in a ruby, the green in an emerald and blue in sapphire and all the other wonderful colours we enjoy in the world of gemstones. What a joyless world we would live in if all we had to choose from were colourless stones!
The group attending the meeting presentation by Alan Hodgkinson
The first stone highlighted in the slideshow was a favourite among jewelers, the elusive alexandrite! One would think that the most intriguing aspect of this phenomenal stone would be the colour change. He gave us a different perspective in that it isn’t the stone that changes colour, it’s the light source that changes the colour. Indeed, he is correct. Further, an even more unusual character behavior is the fact that the stone is trichroic! Most of us don’t even consider this when viewing the stone. We simply look for the change and move on. This stone has a “traffic light” configuration with the trichroism being red, amber and green, depending on the direction viewed.
Dr. Hodgkinson shared with us an incident when he nearly confused an alexandrite with a ruby because he only viewed it under a tungsten bulb. The stone in question was remarkably similar to some other rubies he was working with. He did a refractive index and discovered that it was biaxial and not uniaxial as the corundum would be. This was confusing as he had already decided he had a ruby. After walking outside into daylight, the stone changed to green! His point was to observe all behaviour when taking RI’s and not just the difference in the movement. Another easy confusion is between amethyst and scapolite. Both are uniaxial but the quartz is positive and the scapolite is negative. He also recommended that RI’s be taken out to the third decimal place for a more accurate identification.
Alan drawing the winning 50/50 ticket at meeting
He also mentioned the use of filters for assisting in identifying emeralds, natural and synthetic and dyed or stained jadeite. He has recently developed two filters along with Dr. Hanneman. The jadeite filter will turn a stained green stone red. The same for some synthetic emeralds with exceptions being some Russian and Biron stones. He indicated that a spectroscope would easily separate the Biron, now Tairus stones.
Bobby & Theresa with Alan & Charlotte at meeting’s end
Opals were highlighted by showing examples of natural stones that had the lizard skin or chickenwire appearance under magnification. He showed examples of atypical opals that were green and yellow, resembling chrysoprase. He also informed us that synthetic opal is now being produced in such thickness that the coloumns of colour can be cut horizontally and used for assembled stones.
He finished with a bit of Scottish gemology by teaching that there is a polarized strip in the sky and all we need is a second polarized lens, i.e. sunglasses, to make our own, always present, polariscope!
Dinner upstairs with Alan & Charlote
Photos by Bobby Mann