January 2011
OPL products carry a well-deserved reputation, and ordering some is basically an investment in itself. By the way, the book (SGT Spectroscopy) is a really handy reference, well-explained.

December 2010
Regarding the spectroscope, the big OPL diffraction grating units are the best, particularly for seeing the 450 nm complex in sapphire (prism units stretch the blue and violet, making it tougher to see weak lines in that region).
Dick Hughes

November 2010
Your book is absolutely amazing and even better than I imagined! It's an easy read (even for a foreigner who aren't the strongest in languages), it's very descriptive, extremely educational and I love the humour which sneak in here and there. Furthermore Hilary's illustrations are absolutely fantastic! Your little book has quickly become one of my favourites. I couldn't imagine a better guide. A real gem in my collection. It's not often I get a chance to thank an author and an illustrator directly, but here I'm jumping at the opportunity. THANK YOU BOTH, for a marvelous book, for teaching me new exciting things and for making it an easy joy starring at dark bands in a "rainbow" :o)

November 2010
Amazingly I have grown even happier for your book since my last mail. While comparing what I see in my little cheap spectroscope with Hilary's fantastic artwork, I've really come to appreciate the incredible amount of details you've managed to capture. It's a huge help! I've found quite a lot of very very weak lines, especially in light stones, because I knew where to look, and the paper tip are very handy in finding these weak lines as well. The little descriptions are also their weight worth in gold. I have found a single shortcoming, though. I really think this book should come with a severe warning about the addictiveness of spectroscopy.

November 2010
Thank you again excellent customer service....... and also fine instruments.

July 2010
Thank you for your prompt service. All looks great, now just have to study up on how to use them... so glad I purchased the book as well.

June 2010
It would be a great honor for me to receive an autographed copy of your book! It appears your work is highly regarded since I checked with those whom I respect and your book was the only one suggested as the best.

March 2010
I was so surprised when I got home from work yesterday and Fed Ex came with my package! I was expecting it to take a week or so. Thank you so much for getting it out so quickly. I have spent all morning reading your book and making my first attempts at using the spectroscope. I appreciate all you help.

January 2010
All three (packages) arrived in good order thanks to your/someone's excellent packaging skills. They were all so well padded and wrapped obviously by a very experienced packer, and it was very exciting demummifying them to find the instruments intact. So thank you, and especially for having to fiddle around with three separate packages. Julie

April 2008

Hi Colin, I have heard these are the BEST spectroscopes out there and I need to build my lab since I'm a distant ed. student at GIA, Carlsbad
Thank you!

April 2008
Hello, I would like to buy the opl teaching spectroscope and the 'little' book to accompany it. Highly recommended by the folks on gemologyonline.com.


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