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Jewelry, Gems, & Minerals/Stamp markings on inside of rings.


Hello. I just bought a diamond ring and the band is sterling silver. The total diamond weight is 1/4 of a caret.  Stamped on the inside of the ban
d there are two stamps. 925 is one stamp and I know that it refers to the silver content. The second stamp is the letters. UD.  Can you please tell me what the UD letters / stamp refer to, or what they mean?  Thank you in advance for taking the time to read my post and getting back to me.  Have a nice Holiday.  Ric F.

Answering letter codes on jewelry is NOT my expertise. While the 925 definitely is the silver content of the metal, as far as the UD stamp is concerned I could take an educated guess. UD maybe the manufacturer "Ultra Diamonds" which now is Kay Jewelers. But this is just a hunch.  

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Uwe Richard Kackstaetter, Ph.D. (Dr.K)


I can answer questions concerning minerals, mineralogy, gems, metals, and anything that has to do with geology. However, I am NOT a jeweler. Questions about values, settings, gem stone cuts and appraisals are best directed to other experts on this site. I can however aide in the identification of unknown mineral materials. As a public service and part as training for new geoscientists, our university department provides FREE mineral identification for individuals. Please contact me for details or go to for details..


I am a professor of applied geology and mineralogy with many hours of field experience. Furthermore, I enjoy recreational gold prospecting and mineral collecting. As a professor I am engaged in research concerning minerals and their occurrence.

Member of the GPAA (Gold Prospectors Association of America) as well as the Association of Environmental Geochemists. Member of the GSA (Geologic Society of America) Member of the AIPG (American Institute of Professional Geologists)

Here is a small sampling: Mineral-rock handbook: Rapid-easy mineral-rock determination : written for anyone interested in minerals and rocks - Proctor, Peterson, and Kackstaetter;Macmillan Pub. Co. (New York and Toronto and New York) Physical Geology Laboratory e-Manual [CD-ROM], Kackstaetter, Earth Science Education LLC Colorado Front Range Self-guided Geology Field Trips, Kackstaetter,

Ph.D. in Applied Geology and Mineralogy. I am actively teaching courses in mineralogy and a variety of field courses with mineral collecting opportunities. Background in precious metal exploration.

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