I just saw a jewelry piece that the artist said she “heat-sugared”…
can anyone tell what this process is an how to do it? thx, brenda
Was that an opal that was sugared?
Check out this article in the archives by Katherine Palochak dated
Feb 9, 2005:
Debby
I have heard a jeweller refer to shattered stones due to heat as
sugared.
Opals that are very light and do not show nice flashy colours much
can be “sugared” - its a sugar and acid combination that I know not
much about at all. Except that the opal that results is dark. Other
treatments use oil for the same purpose. Someone out there probably
knows a great deal more than I do and can take it from here.
I heard, or maybe read, somewhere, that the old-fashioned method of
creating black onyx was to steep chalcedony in honey for some months
before plunging it in concentrated H2SO4. The acid attacked the
honey and the heat generated carbonised the sugar, turning it black.
Hence black onyx.
Maybe apocryphal, but interesting.
Regards, Gary Wooding
I’ve bought opal rough treated in this way, soaked in a sugar
solution then treated with sulfuric acid to carbonize the sugar.
Makes a dark opal and the color (often pinpoint color) is enhanced.
Nasty when they do it to rough, you start to grind the opal and it
is white low grade stuff under a surface skin. Finished stones
treated this way look OK, or wrapped in oily newspaper and heated
until they turn dark (risky, cool slowly!) This is nothing new, has
been practiced for years, should be disclosed when you are buying or
selling these stones.
Ben Brauchler
BenzGemz.com
Example of a useless post, If I may be so blunt. If someone feels it
necessary to state something to the effect that they really don’t
know much, if anything, about the subject, perhaps it would be
better if they didn’t say anything at all and just wait to read posts
from someone who does. End of rant.
Jerry in Kodiak
The acid attacked the honey and the heat generated carbonised the sugar, turning it black.
No heat needed. The acid itself carbonizes the sugar. Honey was one
sugar, but not the only sugar or organic material used this way to
produce black onyx/chalcedony.
Peter
By the way Peter, you are correct that the acid need not be heated
but, hot acid ‘encourages’ the carbonization to a greater depth and
it seems to work a bit faster. Kind of like cold pickle will also do
the job but hot pickle works faster.
Cheers, Don in SOFL
I agree with you Jerry.
In fact, this sugaring process has been used for many years, usually
to darken the Andamooka opals from Australia which are a light cream
color in the rough. The opalescence is created in a coarse sand
stone which are porous (well most of them are). The blackening
process does not work on just any opal, in fact if it is used on
common white opal, it often (usually) turns out an ugly stone with
black streaks or blotches. The Andamooka stones, on the other hand,
will normally come out a beautiful even dark brown to dark black
depending on the consistency of the stone. Even then some of them
will not ‘take’ the blackening and will not darken. I have had them
simply refuse to allow the sugared water to penetrate. The color is
usually more than a surface treatment and often goes several
millimeters into the stone but, again, this depends on the nature of
the stone. Normally, the stone is cut to at least the 600 grit level
and then treated after which they are given a pre-polish and polish.
They can make beautiful stones when excellent play of color.
Cheers, Don in SOFL
Barbara, Blackening of opal works best with matrix opal (opalized
sandstone, or sandstone with opal filling the spaces between the
grains of sand). The grey or white matrix opals are soaked in sugar
until the sugar penetrates into the pores and fissures, then soaked
in sulphuric acid which turns the sugar into a black carbon. The
blackened backround makes the colour of the opal stand out. This
blackening process has been used for (I guess) a hundred years and
disclosure is not regulated very much! Heat and pressure may speed
up the process but traditionally this is not needed.
I think the phrase, ‘Heat-sugared jewelery’, is either a
mis-translation or a new metal finishing process.
Alastair
Concentrated sulphuric acid (which is “oily” in appearance and
fumes) is hydroscopic and actually removes the hydrogen and oxygen
molecules from the sugar leaving behind carbon.
Although honey used to be used these days its a saturated sugar
solution that works best. The change is permanent.
Tony Konrath
brenda, if the gemstone was an opal, it was treated (poorly) with
acid, sugar and a brown paper bag - the surface fire is just that: ‘
surface’. the only time i took a commission with client-supplied
stones was to design a setting for 3 large andamooka opals (always
treated) - which the client said the seller promised were ‘natural’.
it was a nightmare - the opals could not be handled except with
extreme care and the design had to minimize future wear and tear
while the client wore it. i sent the finished piece to the client
with a disclaimer that listed the potential problems with 'sugar’
treatment and my good wishes as it was a 'no return for repairs’
commission. the client was thrilled with the piece and i heard only
good feedback. ive
people, think more now, have no returns later.
I've bought opal rough treated in this way, soaked in a sugar solution then treated with sulfuric acid to carbonize the sugar
As with many of these threads, this seems to have drifted away from
the original question.As I recall, the question had to do with
“jewelry”, not opals and being “sugared” after heating, which of
course would not apply to car bonizing opal.
Jerry in Kodiak
(where the red, “sockeye” salmon are now running in local rivers)
By the way Peter, you are correct that the acid need not be heated but, hot acid 'encourages' the carbonization to a greater depth and it seems to work a bit faster. Kind of like cold pickle will also do the job but hot pickle works faster.
The recipe I saw involved soaking the stone in the sugar solution for
literally months, and in the acid for a week or so at least.
Apparently, those guys weren’t worried about speed. This recipe was
old instructions I saw somewhere of how it used to be done in Idar
Oberstein, if I recall. Not sure, but it was an old traditional
method. I think it was in a small spiral bound book/booklet I bought
a couple decades or more ago about how to dye stones. It’s around
here somewhere, but I didn’t see it immediately on the shelf when I
looked, so I can’t easily go back and check. If I happen to find it,
I’ll follow up on the thread if you like.
Peter
Hi
It is not Andamooka Opal that is treated, it is Andamooka MATRIX
that is treated. There are two types of matrix the creamy, which is
the best, and the sand stone type (rainbow matrix).
Cheers Peter Taubers
andamookaopal.com.au
I think the poster may have been asking about a metal working
technique rather than a treatment for opals. “Sugaring” is a
technique used by native craftsmen (and women) in the U.S.
Southwest.
Honey was one sugar, but not the only sugar or organic material used this way to produce black onyx/chalcedony.
And I’ve heard it said that for black onyx it takes about a year to
do.
Agate used to be soaked in a sugar solution and then either heated
or put into conc sulphuric acid to blacken it and turn it into the
more popular banded onyx. Technique dates back to victorian times
when agate jewellery first became popular in Britain. Most of the
agate was cut either in the UK or at Idar Oberstein in Germany.
Nick Royall