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PostPosted: Fri Apr 16, 2010 5:04 am 
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Location: the Netherlands
Also, Kelli, you must guard yourself from picking up white light that slips past the stone. Use a washer or some blue tak to create a narrow beam of light which is smaller in diameter than the stone you are investigating. You want to look at just the light which passed through the stone... otherwise... no spectrum...

Roll a bit of blue tak into a long shape and wrap it around the stone's girdle. Then use the blue tak to stick the stone onto the light source so that light shines through the stone but not passed it.

Too much light isn't good either. A small maglite with full batteries should do the trick unless it's a really dark stone.


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PostPosted: Fri Apr 16, 2010 7:20 am 
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Aha!! That could be the issue, because white light is definitely slipping through. I'll pick up some blue tak (which I haven't used since university days....tape was not allowed on our walls) and try it. Many thanks! Kelli


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 Post subject: Re: Instruments for GIA distance education student
PostPosted: Sat Mar 21, 2015 6:27 pm 
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Hi, I read the comments about spectroscopes, I have a full size model, made by Philip Harris here in England, a prism model by Beck and a Hartridge model which reads directly in Nanometers. The full size one is rarely used, the Hartridge is useful for very precise measurements but the prism hand model is the one most often used. The three together cost me no more than $400.00 on Ebay. Equally, specific gravity is a property it is very useful to know. I have a Westphal's Balance that has done sterling service but I was sitting by the fire with a glass of wine one evening when the solution to S. G. determinations struck me. I have a pocket milligram balance (cost $12.00 or so on Ebay) and I made a bridge to cover the weighing platform, a small gallows to rest on the weighing platform and support two baskets made of silver wire (that's what I had) suspended one below the other by the finest wire I could draw. These go in a 50 ml beaker standing on the bridge filled with distilled water to half way up the connecting wire. The kit is assembled and the "Tare" button pressed. The stone is placed in the upper basket, this gives the weight in air (W1) the stone is then transferred to the lower basket and any air bubbles brushed off with a fine brush, this gives the weight in water (W2). W1 - W2 gives the volume (V) and W1/V gives the specific gravity. If there is a need for great accuracy the specific gravity of water at the temperature of use can be determined by taking stones of known S.G., determining them again in this rig and working backwards to get an accurate S. G. for water.


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 Post subject: Re: Instruments for GIA distance education student
PostPosted: Mon Mar 23, 2015 12:10 pm 
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Kelbat's aversion to buying Chinese made instruments is laudable but I fear he is about two generations too late. It has been my observation that most tools and instruments are made in China and then rebranded for sale in the west. Very sad, but a natural consequence of persons knowing the price of everything and the value of nothing. If the quality control at this end is tight then one is likely to get a good instrument, if not, one could get anything.
Alan F.


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