Gemstones that don't crack easily?

Jewelry Discussion
1

I don’t usually work with stones when making jewellery but have a
few ideas I want to experiment with for some designs involving
setting stones. I am looking for recommendations for semi-precious
stones that don’t crack, chip or scratch easily. I am especially
looking for translucent stones in the colours deep/dark red, black,
dark blue and purple.

I know one of the jewellery manufacturers I worked for briefly, set
saphires and rubies into waxes for casting - I know that these stones
can withstand high temperatures but what are the limitations? Will
there be some stones that have natural deformities which cause them
to crack when heated? How slowly do they need to be brought up to
heat and back down to room temperature so as not to stress them to
the point of cracking. Also, do rubies and saphires crack, chip or
scratch easily - in general?

Although I don’t often work with stones I have been wanting to get a
comprehensive book about precious and semi-precious stones so that
on the occassions that I do need to set stones I have a reference
guide at hand that will tell me all I could want to know about a
stone before working with it. Basically, I am looking for some sort
of stones bible - has anyone got any recommendations?

Thanks!
RR Jackson

2

Corundum (sapphire and ruby) can withstand high temperature up to
1700 to 2000 celsius so normally there will be no problem in heating
them. We heat thousands carats sapphires in crucibles in the stove to
improve color. But the critical point is to heat step by step and
cool down little by little. Sudden change in temperatures can lead to
crack especially when there are already invisible cracks inside.

Sapphires from different origins have different cleavage properties.
For our sapphires, there is no evident cleavage so the sapphires
don’t crack or chip easily. But sapphire and ruby are also crisp
material, they can be chipped when falling onto the hard ground. In
most cases, the thin girdle part will get chipped.

Alex Yu
Neptune Gem

3

Those who have experimented with firing stones in place in PMC have
found that most lab-grown gemstones will withstand higher
temperatures --I believe lab-grown stones fare better because they
have fewer of the natural cracks and inclusions, and none of the
treatments, that make natural gemstones such a crap shoot when
heated. Plus if one does crack or is otherwise damaged, it’s a
relatively simple matter to replace it with something of like color
and size.

There is a chart at the PMC Guild site compiled by Kevin Whitmore of
Rio Grande that describes the results of his extensive experiments
kiln-firing and torch-firing natural and synthetic colored stones in
place in PMC. You might find this a useful source of information
about various stones and their tolerance to heat. The site is
www.PMCguild.com, look under “Getting Started” and “Technical Data
and Charts” to find it.

Hope this helps!

Suzanne

Suzanne Wade
Writer/Editor
@Suzanne_Wade1
(508) 339-7366
Fax: (928) 563-8255
www.rswade.net

4

Dear RR,

In response to your question:

Although I don't often work with stones I have been wanting to get
a comprehensive book about precious and semi-precious stones so
that on the occasions that I do need to set stones I have a
reference guide at hand that will tell me all I could want to know
about a stone before working with it. Basically, I am looking for
some sort of stones bible - has anyone got any recommendations?

Arthur Skuratowicz and Julie Nash have just published a new book,
“Working with Gemstones: A Bench Jeweler’s Guide,” which gives the
working characteristics of a variety of Each chapter is
dedicated to a specific stone and covers common enhancements and
treatments; how the gem reacts to heat, abrasives, chemicals, and
pressure; how to modify or design a piece to accommodate the gem’s
characteristics; what tools you should have close at hand for that
stone; and advice on cleaning and care. The book is published by
MJSA/AJM Press and costs $34.95 ($29.50 for MJSA members). If you’d
like, we can send you (or any Orchid subscriber) complimentary pdfs
of a sample chapter and the table of contents. All requests for the
pdfs can be sent to Shawna Kulpa at shawnak@mjsainc.com.

Thanks,
Rich Youmans
MJSA
AJM Magazine

Rich Youmans
Director of Communications & Publications
Associate Publisher, AJM
Manufacturing Jewelers and Suppliers of America, Inc.

5 
Basically, I am looking for some sort of stones bible - has anyone
got any recommendations?"

A good reference for around $25.00 (US) is Walter Schumann’s
“Gemstones of the World,” Sterling Publishing Co… NY, . It answers
most questions this non-gemologist has.

Gemstones of the World, Revised Edition
By Walter Schumann

Price $24.95

Media: Hardcover
Manufacturer : Sterling
Release data : 01 October, 2000

Robert Creutz
Weymouth, MA, USA