Back to Ganoksin | FAQ | Contact

Restoring patina on bronze or copper


#1

Help!

I have a customer’s cross which he claims was made in the third
century. Wow 1700 years of petina. The petina is a very even coating
of vers de gris a nice greenish color. That is it was a nice greenish
color. I heated it to about 300 degrees farenheit and it turned
black.

Does Anyone know how to restore its original green color on copper or
bronze?


#2
Does Anyone know how to restore its original green color on copper
or bronze?" 

This recipe comes from a handout titled “Patination and Coloring of
Metals”. I gleaned it from my Father’s collection of notes after he
got out of casting iron and bronze to take up working with stained
glass. While I have not used this particular recipe I have used many
of the other recipes in this handout and they have been accurate.
However I must caution you to proceed at your own risk. You will need
an accurate scale (i.e. triple beam or electronic jeweller’s scale).
Alternately you can multiply all of the ingredients by the same
factor (say x 2) to increase the weights and make weighing more
accurate when using scales that are perhaps not so accurate. I know
this reads like an 12th Century Alchemist’s recipe but here it is
just the same.

Bronze - green patina

6 Fluid ounces Water
1.0 grams - Oxalic Acid (wood bleach)
2.0 grams - Calcium Chloride
1.0 grams - Copper Sulfate
4.7 grams - Ammonium Chloride
4.7 grams - Copper Nitrate

Excercise proper precautions (read this as goggles, apron, rubber
gloves, respirator ect…) when working with these chemicals and
compounds as some of these are corrosive or otherwise hazardous.
You cannot be too careful and while you may look like an alien with
all of this gear on you will be a Live Alien with all of your parts
intact! Clean the metal and apply one coat each day until the desired
patina appears. This can take several coats. Next use a toothbrush
to lightly knock down any excess lumps or high spots that could be
abraded if left in place. If brushing results in a significant
change to the patina re-apply the solution repeatedly until the
desired patina is again achieved. Repeat the brushing step. Once you
have the right patina and have removed the high spots you will need
to set the patina with a coating of beeswax or clear lacquer. This
step is important as it will prevent further oxidation of the metal
that could result in the patina changing color over time.

Note; The beeswax or lacquer will likely make the patina darker.
Usually I recommend experimenting on a piece of metal of the same
composition but it sounds like you may be hard pressed to find
another piece of 4th century “bronze”. :wink:

Note; to make the color brighter leave out the copper sulfate and
oxalic acid. Conversely you can darken the color by adding varying
amounts of these compounds up to the full amount called for in the
basic recipe. I hope this is helpful to you in your quest to restore
and preserve this relic.


#3

rio grande (as well as other suppliers) sell a variety of patinas
and oxidizers. rio grande the # is 335-120 for a pint of MIDAS GREEN
PATINA SOLUTION…and it reads… “use on brass, bronze or copper”

good luck!
-julia


#4

The patina was probably a sulfate – carbonate blend… The green
would probably be the carbonate. You probably destroyed the
effect!! But you might try to get it back by putting it a loose
lidded enclosed container with a moist rag to boost the humidity add
some backing soda to and a mild acid ( dilute vinegar) cap off and
wait. don’t let the piece get wet and be sure you don’t build up
much pressure so as to break the container… wait but don’t hold
your breath…


#5

If in fact the piece you worked on is 1700 years old you will not be
able to match a natural patina that is that old.

You can however add a new patina that will give a brighter green
color than the original in the following manner as taken from the
book Creative Casting by Sharr Choate.

If the metal is Bronze:

Yellow - Green  Patina

ammonium chloride  -  15 ounces
copper acetate  -  8 ounces
water  -  1 quart

Heat the solution to 212 *F and apply to the piece with a brush

If the metal is Copper

Apple Green Patina

ammonia  -  4 fluid ounces
sodium chloride  -  5 ounces
ammonium chloride  -  5 ounces
acetic acid  -  1 quart

Dab the surface until dry.

Hope that helps.
Good Luck
Greg DeMark
email: greg@demarkjewelry.com
Website: www.demarkjewelry.com
Custom Jewelry - Handmade Jewelry - Antique Jewelry


#6

Please refer to the book,

The Colouring, Bronzing and Patination of Metals, by Richard Hughes
and Michael Rowe. This book has extensive recipe references. Please
keep in mind however, that many of the treatments involve dangerous
chemicals.

The Colouring, Bronzing and Patination of Metals
By Richard Hughes

http://www.ganoksin.com/jewelry-books/us/product/0823007626.htm
Price: $53.55

Media: Hardcover
Manufacturer : Watson-Guptill Publications
Release data : 01 February, 1991

Best regards,
Tom Warden
KW Art
Ft.Collins, CO& USA


#7

I really have nothing to offer from my PERSONAL knowledge to the
person who heated the 1700 year-old cross and destroyed the patina -
except to say that it looks like you went out over your depth and I’m
sorry for you, but probably not as sorry as you are.

It reminds me of a few close escapes I have had - like about 40+
years ago when some trusting soul gave me an ancient Chinese cast
bronze drinking vessel, one of those which stands on three legs. One
of the legs had broken about halfway in its length. He asked me to
solder it back together for him. To this day I don’t know how - at
the tender of 22 - I found the shred of common sense to return the
object to him untouched after staring at it for a few days. It turns
out that vessel was far older than the 3rd century cross - I can’t
recall now, but maybe 1500 B.C. Anyway, I shudder to think what I
would have done to the value of the object had I plunged ahead with
what looked like a routine repair. A close call.

You do have some obligations,having gone as far as you have done. If
the ancient cross you have on hand is indeed valuable to the owner -
either in $ or sentimental terms - I would stop right where you are -
do nothing more - and head for the nearest Art Museum which has a
good objects conservator on staff. As it happens, my daughter is one
such person - a specialist in (among other things) early bronzes and
similar objects - and she may have some useful advice for you.
Please email me off the Ganoksin “chat line” (or whatever this thing
is called) and I can put you in touch with her. Or she can put you
in touch with the right person near you. Let me know where you are
located.

Good Luck
Marty in Victoria


#8

Restoring patina on bronze or copper

to obtain a nice green platina then this is how i do it but please
experiment

 1 tbsp ammonium choride
 1 tbsp salt
 1 oz ammonia
 1 qt water

mix the chemicals in a plastic carton or bowl. Warm water will hasten
the dissolving process. Unless your tap water is pure and neutral,
use bottled water. The copper surface must be chemically clean and
dry. Use scotchbright , pumice or a commercial scouring powder. Avoid
steel wool because of its oil content. Spritz the metal with a pump
spray untill it is uniformly wet. Allow it to dry naturally when dry
then respray and again allow it to dry naturally repeat about 4
times

this is a brief guide but please experiment as lots of thing can
effect the out come try it on another piece of metal experiment re
create the annealing process etc

David Baggaley


#9

For an object as ancient, and therefore, one assumes, valuable, may
I encourage you to seek out the advice of a conservator/restorer? If
I were doing that, I guess I would first ask on this forum, then
call one or more of the appropriate museums-- Smithsonian, Field
Museum of Natural History or the Oriental Institute (these two in
Chicago), etc.

Noel


#10

For what it may be worth (maybe not much) I would be skeptical of
the reported age of the piece in question. I’m no expert, but I do
have a few ancient bronze artifacts as well as a couple of pieces
(Chinese) made to pass as Han dynasty originals. None of these
pieces have a GREEN patina, but one much darker, sort of
brown/black. I have several Roman coins dating back some 2,000
years, a couple of very old Chinese bronze mirrors, and as I recall,
the pieces I have seen on display in various museums all have pretty
much the same patina, and it isn’t green. Of course that really
doesn’t make your problem any the less since the customer apparently
THINKS the piece is 1700 years old.