Image by Irene Helm
There are a number of ways to patinate metal (see my past post on 8 Ways to Patina Jewelry).

Some of the ways are stinky - LOS or liver of sulfur (potassium sulfide) and ammonia are two examples  - and also need to be used with care.


Hydrogen sulfide which has the characteristic smell of rotten eggs, is released during the use of liver of sulfur. It's poisonous in large amounts, so good ventilation is vital especially if you oxidize metals a lot.

LOS should be stored well away from any acid.  Pickle (acid) solutions used to clean metals after the soldering are a prime example.  Very dangerous levels of hydrogen sulfide will be created if the LOS is allowed to react with acid solutions.

So if all the above really scares you, rest assured there is a cheap, easy and safe way to patinate your metals. Just use boiled eggs!  Eggs are rich in sulfur-containing amino acids which are the building blocks of proteins.  The aroma of cooked eggs is quite complex but one of the contributing gases emitted is a small amount of hydrogen sulfide. Rotten eggs smell that way because greater amounts of hydrogen sulfide gas are released with bacterial decomposition.

Check out the boiled egg technique tutorial by Irene Helms. It's really neat because she uses just 1 boiled egg in a plastic bag.  It's so much more convenient than putting everything in a jar because she could easily turn over the bag several times to ensure even oxidization.  It took her only 15 minutes to oxidize some silver bails.

However, if you google the technique, there are variable results with this technique. Some, like Irene, say the yolk works better but one person I came across swears by the egg white. Then there are those who can't make it work even after days.

So it's time to put on my scientific hat, er, coat and conduct a  few experiments to sort out some of the discrepancies.

Experimental protocol :
I boiled 5 large eggs by placing them in a pan covered with water. When the water reached boiling, I closed the lid, turned off the heat and let it sit for 20 mins. I rinsed the eggs a few times with cold water.  One egg was boiled the night before and left overnight on the kitchen counter.

The next morning,  the other 4 were boiled and then quickly cooled in cold water. All 5 eggs were halved with a knife, shell and all. The "day-old" and one "fresh" egg were placed in plastic zip lock bags. 2 "fresh" eggs were placed in a lidded glass container and on a saucer respectively. The egg white and yolk were separated for the 5th egg and each component was placed in plastic bags. The eggs were mashed up further using my fingers. 2  round copper beads were used per container - one directly on the egg itself.






The copper beads were closely observed for an hour.  Why an hour?  If there are going to be any useful changes, it should have effectively done so well within the hour. Besides I wasn't keen on having rotting eggs for too long!

What I learned is included in the following :

TIPS

Use Uncoated Metal
This technique will obviously not work for coated metal because the metal is not exposed to the hydrogen sulfide.

Metals to use
The method will work for copper, bronze, brass and sterling silver as the latter contains 92.5% silver/7.5% copper. But it will probably take a long time to oxidize fine silver (99. 9% silver) so don't do it!  Save the fine silver for shiny designs.

Rough Metal surface
Generally a shiny surface will take longer to oxidize than a rough one.  It's too smooth for the process to easily get started. This is the reason why many artisans like to tumble their finished pieces. Not only does it work harden the piece, small surface imperfections are removed so it will take longer to tarnish.

I did not roughen the copper balls I used. Therefore it took longer to "turn" them dark than Irene's textured silver bails.

Hard-boiled Not Soft-boiled Eggs
It's not just that soft boiled eggs would be a runny mess. The longer the cooking time, the stronger the aroma. That's because the egg protein denatures and coagulates with heat and time, releasing its sulfur content in the form of hydrogen sulfide. That means more gas is available for the oxidizing process. Stick your nose to a hard boiled egg next time you cook one and you'll smell what I mean! 

It did not make that much difference using a freshly cooked egg and one that was cooked about 12 hours before hand. The oxidation was visible through the plastic bags within minutes for both. It was slightly faster for a freshly cooked egg in the first 5 minutes. The pictures below show the greyish areas on all the beads. The dark areas are more pronounced for the lower beads which were those placed directly on the mashed eggs and thus closer to the gas release.


Break Up the Egg
Breaking or mashing up the egg into smaller pieces means the boiled egg's surface area is increased, and so is the amount of gas released.

Use a Container
The beads on an open plate failed to oxidize at all because the relatively small amount of gas given off after cooking was not trapped and soon dispersed into the room atmosphere.  They looked exactly like the shiny control (untreated) beads!


Irene's use of a plastic bag is inspired because the space for the gas inside is small so it will fill quicker. But even a larger container will still work as shown by the oxidized beads below. Her method though is good for turning over pieces without opening the container. The gas naturally escapes if you keep opening the container to look!


 If you look at the lower bead shown in the picture above, it was the most oxidized of all the beads. The glass container  had a slight edge on the plastic bag method because the static cling around the beads probably excluded access to the gas.  I had to frequently move the beads in the plastic bags to counteract the static cling. If you are going to use plastic bags, try coating them inside with a small amount of baby powder before using them.  It'll prevent the sides of the plastic bags from sticking together.

Whole Egg Or Whites, Not Yolks
This tutorial on Wikihow advocates the use of a rack to hold the metal pieces above the egg yolk.  The position makes sense as the gas will rise up. However, I suspect the reason why it took a day or so for this method to work is the use of only the yolk.

Sulfur is indeed yellow in color so many people mistakenly think the yolks are sulfur rich. Egg yolks are that sunny hue not because of sulfur but organic pigments called carotenoids. The sulfur present in eggs exist not as the free element but as disulphide bonds linking amino acids. These weak bonds break up during cooking.

According to Harold McGee (see reference below), most of the hydrogen sulfide forms in the egg white. So was he right? Yep. The pictures below are proof. The egg yolk only beads had almost no sign of oxidation unlike the egg white ones after 1 hour.


So use either the whole egg or just the white.  McGee also says older eggs will generate more hydrogen sulfide. Also, if you have a lot of metal to oxidize, one egg may not be enough.

Would you eat the egg afterwards?  I let you be the judge! Here is the egg white after I removed the copper bead :


References
Patination Safety Considerations 
Harold McGee (2004) On Food and Cooking: The Science and Lore of the Kitchen Excerpt
Wikipedia : Egg Yolk


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