Administered by Hale Sweeny (firstname.lastname@example.org)
This list digest contains the following message subjects:
1. LapDigest Issue No. 130 - Tuesday 3/31/95
2. NEW: Question on Indices and Archive Searching
3. RE: Walking Vibratory Tumbler
4. Re: Walking Vibratory Tumbler
5. NEW: Coloring Agate Slices--Historical German Method
Subject: LapDigest Issue No. 130 - Tuesday 3/31/95
This is my birthday, so I am soliciting a major birthday
present! Who among you would like to write about a page of
so on how to turn lapidary rough into bowls and tumblers? I
would appreciate it and I know most of the list would, too!
That would be a GREAT birthday present. So if you want to
volunteer to do so, please write and let me know.
And if you have a specialty in lapidary you could write up,
I'd appreciate that, too! Just let me know.
The book list is coming along and will be published when
finished. Still looking for more volunteers to write reviews
of lapidary books - not in depth, but a general review
telling what is in the books and if you would recommend it
for reading. If you want to give me another present, just
write and say you will do one or two reviews yourself.
And please don't forget to write "non-commercial republish
permission granted" on the bottom of each of your posts. This
will allow club bulletin editors to copy items into their
club bulletins, without copyright concerns.
The first letter below indicates that many of you don't know
how to search the Archives. I have begun a write-up which
will describe how to search the Archives; it will be published
Now for an apology: I mistakenly ascribed the last letter in
the last issue to Rose McArthur. She wrote and said she was
not responsible -- said she was NOT guilty. I apologize to
whoever's name got erroneously miswritten as 'ROSE'. Sorry.
Have no idea how it happened!! Why don't you write and tell
me just who it was I insulted!!(smile). I'll apologize again!
Take care, and HAVE FUN!!!
Subject: NEW: Question on Indices and Archive Searching
Hale.. I asked for a directory and received it but really
can't tell just what is on most of the files. The
description on many just give the index number but not
contents. Is there some way I can get the contents of all
files so I can print and file those I want for future
Also, what are the number sequences on the right of the index
screen? I missed a lot of the digests this fall and winter
when we were traveling but I think what you are doing is the
greatest thing since sliced bread. Will you be at Holland
this fall? I am expecting to take my first opal cutting
class with Joe DiPetrio. Have been going to Wildacres the
last few years but heard that Joe was excellent for opal.
Hope Anne is doing OK. Our best to you both.
Herb Jones PDGMS
Herb: I suggest you ask for Index3.txt. This is an index of
the threads which have appeared. For example, near the top of
the index, we see four lines, all of which are labeled:
'Technique to Fill Flaws'. This is a thread, or a single
topic of discussion. The first line, labeled 'NEW', refers to
the original question. The number 6-2, also on the first
line, means that the original question appeared as the second
item in Issue #6. Then the next three lines refer to the
three responses received, each with a reference as to where
the response is located (Issue No., Item No.). Below these is
the item: (FillingFlaws.txt), which means that the thread has
been reproduced and summarized as a file and is in the
archives and is named 'fillingflaws.txt', which you may order
with a simple GET command.
Hope this helps! And thanks for your expression of concern.
Hope to see you at Wm. Holland.
Subject: RE: Walking Vibratory Tumbler
I run two (2) 10 lb vibrating tumblers sold by Tagit. I had
the same "walking" problem as you until I slid a piece of
carpeting underneath all four legs. Problem solved!
Subject: Re: Walking Vibratory Tumbler
One of the joys of the computer age that works well with
tumblers is old mouse pads. That's what I use under my rotary
tumbler to keep the noise from driving me mad. It should also
work well under a vibratory tumbler.
Subject: NEW: Coloring Agate Slices--Historical German Method
Back in 1913, Dr. O. Dreher, who worked at Idar in agate
cutting, published a small paper on how agate slices were
colored by them. This was astounding, as the methods were
considered a trade secret at that center. Most of the early
papers in English were based on translations of that paper.
I am presenting it for historical and general interest to the
lapidary community. I beg you not to try his methods, as
they are without the safeguards we would employ today, and
use crude and unrefined chamicals. It is being printed solely
for historical interest (and as there were so few postings
from the members, today).
There will surely be much disapproval, from the gem-cutting
industry, through the publication of this paper. While some
of the techniques given here may not be generally known, it
is understood that the general principles are not a secret to
those outside the industry. Further, one can not learn in the
coloring of agates and other stones merely by reading a paper;
practice plays an important part in gaining results.
An apprentice in the agate-cutting industry is often taught
only the cutting and polishing, while the "secrets" of
coloring as practiced by his master will be guarded from the
student. The young cutter busies himself with experiments in
new methods, and often introduces an improved technic.
Therefore, I believe it would be of value to the industry in
general if the apprentice cutter was fully informed on the
standard means of coloring and beat treatment of ornamental
This brief pamphlet is not intended as a complete text on
stone coloring. It will only give some principles on which
the beginner can go. The use of many local expressions I
consider desirable. Valuable instructions were given me by
my father, likewise by August Dreher and Gustave Zang; my
thanks to them at this point.
The coloring of agates depends on the introduction of a
coloring matter into their pores. Some layers of agate are
less porous and therefore these will not absorb pigments but
remain wholly uncolored or only partially colored. The cutter
calls the less porous layers in the agate 'hard'. The layers
or bands readily colored are termed 'soft'. The skilled
artisan can often judge the ability of an agate to absorb
pigments, prior to the treatment. The art of coloring agates
and similar stones has been known to us for only a relatively
short time. Long ago the Romans had learned the secret of
black colors but they kept this secret for centuries. Finally
in 1819 this old Roman technic was discovered by accident.
Lessons From Nature
Along about 1813 some German cutters observed agates in the
field, presumably colored by the action of sunlight. Agates
which projected from the earth were often colored a carnelian
or sard (reddish), while the remainder of the stone beneath
would be entirely colorless. This led to the practice of
"burning" colorless agates to produce the reddish colors.
Not all colorless agates will become reddish when given the
heat treatment of "burning." It is thought that the agates
which fail to respond are those lacking in iron compounds,
present as an impurity. This was finally solved by soaking
the agate in a soluble iron salt and then "burning" by oven
treatment. In 1845 the method of blue coloring was discovered
and in 1853 green colorings were introduced, all the result
of experiment by the lapidarist.
The manner in which the coloring pigment is introduced into
the agate varies according to the color desired. In all cases
where a permanent color is attained, the coloring matter is
not introduced in a dissolved form directly, but by the use
of various chemical reactions; these take place within the
In general there are two methods of coloring an agate. In one
case the soluble metallic salt is permitted to soak into the
pores of the agate. This soluble salt in turn is changed to a
colored insoluble oxide by heating. In the other method, two
solutions or 'baths' are used in succession, the second bath
causing a colored precipitate of an insoluble metallic salt
to be deposited within the agate.
The following will serve to illustrate how some of the colors
can be obtained in an agate:
Red: Soaking stone in iron nitrate solution and then by
burning", an iron oxide is produced.
Bluish Green: Soaking in solution of chromic acid or
ammonium bichromate, and heating to produce a chrome oxide.
Apple Green: Soak in nickel nitrate and "burn" to produce a
Brown: Soak in a sugar solution and heat strongly to
carbonize sugar to caramel.
Blue: Soak in bath of yellow prussiate of potassium and then
in a solution of iron sulphate to precipitate "Berlin blue."
Blue: Soak in solution of red prussiate of potassium and
then in solution of iron sulphate to precipitate "Turn-bull
blue" in agate.
Black: Soak in sugar solution and then in sulphuric acid, to
change sugar to carbon.
For completeness it may be mentioned that aniline dyes have
been used to some extent in the artificial coloring of agates.
The aniline colors, however, are not as permanent as the
metallic oxides and precipitates described above. Aniline
tends to fade when exposed to strong light.
Before the agate is colored it must be cleaned of all oil
and impurities which may be adhering to or soaked into the
stone. In the cutting of agates, oil or kerosene is used to
lubricate the saws, and this must be first "extracted." The
petroleum substances can be removed by boiling in a strong
solution of sodium bicarbonite, or solvents like gasoline or
some non-inflammable commercial cleaning fluid can be used
The agate may carry a small amount of iron and it is desired
to remove this prior to "burning" for green colors, otherwise
a dull or muddy green may be obtained. To remove iron
compounds the stone is placed in warm nitric acid for two or
three days and then placed in warm water for several days.
The purpose of the nitric acid is to render any iron present
soluble, so the water soaking may remove same. The warm water
bath should be changed a number of times.
Important Colors -Red
The knowledge of obtaining carnelian and sard (reddish)
colors in agate by "dry burning" was first discovered in 1813,
but the "bath" method of obtaining the red shades came later,
and at uncertain date.
(ASIDE: At this point, Dr. Dreher describes how they made a
solution of iron nitrate by using about half a pound of iron
nails and about a quart of nitric acid. Today we can buy
refined iron nitrate salt and dissolve this in water, for use
as described below.)
To produce red colors the agate is soaked in a strong solution
of iron nitrate. According to the directions of the old German
agate cutters, this solution should be as thin as Munich beer.
The aquaeous solution of iron nitrate should be kept warm and
the agate submerged for from one to four weeks according to
the thickness of the stone. Stones three millimeters thick:
for about a week; six millimeters: about three weeks and ten
millimeter stones: about four weeks. Stones thicker than ten
millimeters will seldom color throughout. (A millimeter is
1/25 of an inch.) This means that seldom will the color
penetrate into an agate deeper than about five millimeters,
or about 1/5 of an inch. Let it be understood at this point
that all coloring is done after the stone or slab is
completely cut and polished, otherwise grinding would expose
the uncolored material below.
After the agate has been soaked in the above solution for the
desired time, it should first be carefully dried in a warm
oven for from two to ten days. This is to remove as much free
moisture as possible prior to the "burning" to avoid possible
The agate is removed from the oven and while still warm is
placed in a crucible. The agates can be best packed in some
substance like fibrous asbestos or powdered magnesium oxide,
and the crucible covered (an iron crucible will do nicely). The
heat in the oven is raised very slowly, until the crucible
has reached a red heat. It is then allowed to cool very
slowly. This is best carried out by reducing the flame or
heat gradually. The agate must not be removed from the
crucible until the contents are completely cooled. It is
possible that some stones may not have the desired color. In
this case the soaking in the iron nitrate solution and the
oven "burning" can be repeated one or more times as desired.
Green colors can be produced in a number of ways. Two
"baths" in common employ saturated or strong solutions of
chromic acid or potassium bichromate. The solution of
chromic acid seems to be preferred, though the bichromate
salt is cheaper. The stone is placed in the chromic acid
solution for from eight to fourteen days, according to the
thickness and the "hardness" of the agate. Stones or slabs
over ten millimeters in thickness should remain in the bath
for a longer time six to eight weeks. The stones are then
removed from the bath and placed in a warm closed container
with lumps of ammonium carbonate, for at least two weeks. The
purpose here is to have the ammonia gas penetrate the agate
and cause a bright green precipitate of a chromate salt.
(Liquid ammonia solution would possibly bleach out some of
the soluble chromic acid or bichromate). After the agate is
removed from the ammonia gas chamber it is dried and then
gradually strongly heated in a crucible and oven as described
under red coloring.
As water evaporates from the warm solution additional water
can be added. The agate is removed from the sugar solution
and without washing is placed in sulphuric acid. Green colors
often do not come up to expectations. A muddy green or
bluish-green may be noted. Experiments will often solve the
problem in various kinds of agate. Of the best methods so far
as I know them, I dare not say anything, since they should yet
Black - Carbon
Black coloring was first known to the Idar cutters in 1819,
and was discovered in an accidental manner. The agate is
first soaked in a solution of ordinary sugar, 375 grams to
one liter of water, or about as thick as flowing honey. The
earlier cutters employed diluted honey, hence this solution
is often called the honey bath. While the agate is in the
sugar solution the vessels should be kept warm, as this
seems to promote penetration. The stone is kept submerged for
from one week to three weeks, according to thickness,
"hardness," and depth of color desired. As water evaporates
from the warm solution additional water can be added. The
agate is removed from the sugar solution and without washing
is placed in sulphuric acid. The acid is slowly warmed and
then brought to a boiling or near the boiling point for about
fifteen minutes. The vessel should be covered and care should
be exercised to avoid the hot acid from spattering in the
eyes, skin or clothing. A large vessel is best and a hot
plate where the heat can be controlled is excellent. The
agate is permitted to cool with the acid for a few hours.
After the sulphuric acid treatment, a stone may tend to
"sweat," due to a small amount of acid remaining in the pores
of the agate. This can be eliminated by soaking the agate in
warm water for several hours of longer.
Blue coloring was first used at Idar in 1845. Two shades of
blue can be had, by the use of yellow prussiate of potassium
or by the use of the red prussiate of potassium
(ferrocyanides of potassium). Dissolve 250 grams of one of
(WARNING - poisonous) in one liter of water. The agate is
soaked in this solution for from one week to two weeks. This
bath should be kept warm, not too hot and should not be
boiled. The agate is then soaked in a solution of iron
vitriol (iron sulphate) for from four to eight days according
to the depth of color desired. No "burning" is needed in this
A darker blue color will be had if the iron sulphate
solution is acidified with a few drops of sulphuric and
nitric acid. While the agate is in the iron sulphate
solution it can be examined from time to time, and removed
when the desired color is noted. The solutions used in agate
coloring can be used repeatedly, by adding water to replace
evaporation and small amounts of the salts as the liquid
Some of the chemicals employed in agate coloring are
poisonous or corrosive and should be used with due caution.
In the use of the prussiate of potassium solutions, small
amounts of cyanide gas may be generated and care should be
used in the inhalation of these fumes. This can be best used
in a chemical laboratory under a hood, or outdoors where the
fumes can not reach a possibly dangerous concentration. Much
of the agate dyeing in Germany is done in the homes of the
cutters; the kitchen of the Idar, Germany, agate cutter is
often lined with various vessels where stones are receiving
their beauty baths.
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