RockHoundBlog

chemical vapor deposition (CVD) diamonds- Growing diamonds (colorless and pure)

Filed under: how to?,regular postings — Gary February 24, 2007 @ 10:44 pm

CVD_diamond One of Apollo’s made diamonds.

“When I came in Monday, I couldn’t see the (stone) in the beaker,” Linares says. The diamond was colorless and pure. “That’s when I realized we could do gemstones.”

Apollo Diamond is making real diamonds through a process called chemical vapor deposition (CVD). Here is an explanation of the process:

(1) A slice of diamond is placed flat inside a chamber. Hydrogen and hydrocarbon gases are injected and heated to thousands of degrees at the right pressure.
(2) Carbon atoms land on the diamond slice and replicate the crystal’s structure, the way a drop of water merges seamlessly into a pool of water. The diamond grows thicker and taller. Growing a 5 carat diamond can take a week.
(3) The top can be sliced off and cut into gems. Or the diamond can be cut into thin wafers for computer chips or other uses. Part of the slice is returned to the chamber to make the next diamond.

“We basically grow our own raw material,” says Apollo president Bryant Linares.

Source: Apollo Diamond

Two different paths to diamonds

In 1955, General Electric figured out how to use room-size machines to put carbon under extremely high pressure and make diamond dust and chips. The diamond material wasn’t pure or big enough for gems or digital technology. But it had industrial uses, such as diamond-tipped saws. Such saws made it possible, for instance, to cut granite into countertops.

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Faceting Quartz- Rock Crystal, Amethyst, Citrine, Ametrine and Smoky Quartz

Filed under: how to?,regular postings — Gary February 16, 2007 @ 4:14 pm

I have been asked a couple times about faceting (how to) – here is one of many articles to come about the subject-

Faceting-Quartz

Australian faceter Arch Morrison -

There are five main transparent varieties of Quartz which are used for faceting.
These are the clear Rock Crystal and the coloured Amethyst, Citrine,Ametrine and
Smoky Quartz. Quartz has no cleavage problem and the birefringence of Rock
Crystal is so small (.009) that the rough can be oriented in whatever direction
gives the biggest final stone.There is distinct pleochroism in the deep-coloured
varieties which places some restriction on orientation for best colour. Orient
by looking through the rough at a light source and rotating till you have best
colour. Place the Table at right angles to this plane. Where the coloured rough
has zones or bands of colour the usual solutions apply. [put the spot zones in
the Culet and the banding planes parallel to, and just below, the Girdle].
Quartz doesn’t have a temperature problem so wax dopping can be used if desired.

For cutting a Quartz SRB the standard angles recommended by Vargas of 43 degrees
for the Pavilion Culet facet and 42 degrees for the Crown Main work well.
However, it is necessary to ensure that any other cut has been designed for
Quartz and is capable of handling Quartz’s fairly low RI of 1.54. [if the cut
is designed for a higher RI then it will window in Quartz].

When I volunteered to do this post on Quartz I did so with some trepidation.
Quartz has probably had more internet discussion than any other faceting
material. Everybody has cut it and everybody has the sure-fire way to get the
absolute best finish. It is not the cutting which causes the problem – any
reasonable sequence of progressively finer cutting laps will do the job and it
will depend on what laps you have in your arsenal. I use a 260 Mesh lap for
initial rough shaping and move as soon as possible to 600 Grit for cutting, 1200
Grit for fine finish [although sometimes 3000 or 8000 diamond prepolish becomes
necessary] and then on to polishing.

Polishing is where the different opinions surface. Some people swear by the
Lucite lap or the ultralap – others swear at them. Cerium Oxide seems to be the
polishing medium most preferred …but not always.

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excellent agate article, includes staining agates, interesting!

Filed under: how to?,regular postings — Gary February 14, 2007 @ 11:28 pm

agate_staining

AGATE, a term applied not to a distinct mineral species, but to an aggregate of various forms of silica, chiefly Chalcedony (q.v..) According to Theophrastus the agate (achates) was named from the river Achates, now the Drillo, in Sicily, where the stone was originally found.  Most agates occur as nodules in eruptive rocks, or ancient lavas, where they represent cavities originally produced by the disengagement of vapor in the molten mass, and since filled, wholly or partially, by siliceous matter deposited in regular layers upon the walls.  Such agates, when cut transversely, exhibit a succession of parallel lines, often of extreme tenuity, giving a banded appearance to the section, whence such stones are known as banded agate, riband agate and striped agate.  Certain agates also occur, to a limited extent, in veins, of which a notable example is the beautiful brecciated agate of Schlottwitz, near Wesenstein in Saxony—a stone mostly composed of angular fragments of agate cemented with amethystine quartz.

Most commercial agate is artificially stained, so that stones naturally unattractive by their dull grey tints come to be valuable for ornamental purposes.  The art of staining the stone is believed to be very ancient.  Possibly referred to by Pliny (bk. xxxvii. cap. 75), it was certainly practiced at an early date by the Italian cameo-workers, and from Italy a knowledge of the art—long kept secret and practiced traditionally—passed in the early part of the 19th century to the agate-workers in Germany, by whom it has since been greatly developed.  The coloring matter is absorbed by the porosity of the stone, but different stones and even different layers in the same stone exhibit great variation in absorptive power.  The Brazilian agates lend themselves readily to coloration, while the German agates are much less receptive.

To produce a dark brown or black color, the stone is kept perhaps for two or three weeks in a saccharine solution, or in olive oil, at a moderate temperature.  After removal from this medium, the agate is well washed and then digested for a short time in sulphuric acid, which entering the pores chars or carbonizes the absorbed sugar or oil.  Certain layers of chalcedony are practically impermeable, and these consequently remain uncolored, so that an alternation of dark and white bands is obtained, thus giving rise to an onyx.  If stained too dark, the color may be “drawn,” or lightened, by the action of nitric acid.

Agate is stained red, so as to form carnelian and sardonyx, by means of ferric oxide.  This may be derived from any iron compound naturally present in the stone, especially from limonite by dehydration on baking.  Some stones are “burnt” by mere exposure to the heat of the sun, whereby the brown color passes to red.  Usually, however, an iron-salt, like ferrous sulphate, is artificially introduced in solution and then decomposed by heat, so as to form in the pores a rich red pigment.

A blue color, supposed to render the agate rather like lapis lazuli, is produced by using first an iron salt and then a solution of ferrocyanide or ferricyanide of potassium; a green color, like that of chrysoprase, is obtained by means of salts of nickel or of chromium; and a yellow tint is developed by the action of hydrochloric acid.

read whole article here: http://www.djmcadam.com/agate.html

Carving Amber – step by step

Filed under: how to?,regular postings — Gary February 7, 2007 @ 2:58 pm

Carving Amber
By Yoli Rose
Beginner-to-intermediate carving project.

amber

I found this interesting “how to” article at Lapidary Journal…

There is something warm and delicious about amber, the fossil resin of ancient pine trees. A carved piece of amber catches and plays with light, and has a smooth, sensuous feel. It is soft (2-3 on the Mohs scale) and relatively easy to carve – you can use everyday tools and do it by hand, or use a flexible-shaft machine, as I will describe here. It helps to not get too attached to a piece because amber is brittle and can chip or break, and it cannot take heat.

read article here http://www.lapidaryjournal.com/jj/899jj.cfm

Introduction to Faceting From The Image. Rockhound, Gems, Jewelry, step by step

Filed under: how to?,regular postings — Gary January 5, 2007 @ 3:15 am

Faceting

I was asked this year to give an introduction to faceting class at the Michigan Geology and Gemological Society seminar weekend. While I do not consider myself to be a “big” faceter (actually on a per pound basis I guess I am), I do enjoy cutting an occasional piece of rough. So I decided to use my other hobbies 3D Animation and digital photography to tell the story.

I am not a fan of any current presentation software on the market (PowerPoint in particular) so I have taken to using the WEB to put together presentations and provide resource material to others. This also allows me to get double use of the material.

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Rock Tumbling – how to guide, Tumbling procedures, Step by Step. Lapidary

Filed under: how to?,regular postings — Gary December 22, 2006 @ 1:21 am

rock_tumbler rock_tumbler_grit
TUMBLING
PROCEDURES
If you haven’t tumbled stones before,
or need a refresher,
these procedures may be of interest to you:
PREPARATION

  1. Wash the stones thoroughly. Be sure there is no debris attached to the stones. Use a brush and soapy water if necessary.
  2. Sort your stones by size and hardness into groups or batches. Soft stones will grind away before hard stones are ready for the next step. Stones of nearly the same size will have more points of contact and therefore will produce a more thorough and faster grinding action. If certain shapes or sizes are desired, you may want to preform your stones by grinding them on a lap first.
    COARSE GRIND
  3. The amount of stones put in a tumbler barrel depends on the size of the barrel and the stones themselves. The best tumbling action occurs when the barrel is filled 50% to 60% of its capacity. Fill the barrel with your stones to 1/2″ above the half-way mark. Remove the stones and weigh them. This weight will help you to determine how much grit is needed. Record this weight for future reference. Use the following ratio to determine the amount of silicon carbide grit needed for your batch: (more…)