My patination attempts are kind of frustrating

[Brian Brown]

So in the last 6 months, when I have been able to get a few minutes, I have tried my hand at leafing, and patination. I first tried copper leaf. I used a sea sponge to put on sodium sulfide, and really liked the results (dark reds and mostly browns), just not with the wood color that it was on. So I tried to add some cupric nitrate with ammonium chloride. That created a beautiful green blue patina, which is what I wanted in the first place. Not only was the color great, but it worked really well over the browns and reds. I let is sit for a couple of weeks, to see what would happen. It continued to get greener/bluer at a very slow rate. When it arrived at the stage I wanted it to be, (and about the point where it stopped changing), I decided to put a finish on it. David Marks suggests lacquer, so I gave it a very light coat of rattle can lacquer. The green patina disappeared instantly when the lacquer hit it. It left the brown, and the red darkened considerably. Now, two weeks later, the patina has darkened some more under the lacquer. It was getting too dark feeling for the wood, so I put some random shaped copper flakes on the surface, put a small amount of sodium sulfide on to blend the edges, and am now waiting to see the patina change. I hope this works.

I also tried some dutch gold leaf on a similar bowl. I made a test board with the dutch leaf. I dabbed a section of the gold with Cupric nitrate, mixed with ammonium chloride, and nothing happened. After an hour it turned an almost imperceptible green color. I dabbed another section with sodium sulfide, and it immediately turned an orange color. According to DJ Marks, it will turn various shades of red, green, and blue, but mine seems to be stuck on orange. Maybe I am just too impatient.

So this brings up some questions.

Everything I have read suggests not removing the acids, just covering them over with final finish to seal them. How will this affect long term stability? In most art mediums, we try to avoid acids in our materials because they are severely detrimental to the archival stability of artworks.

Is it a problem to wash the surface after the patination has reached an acceptable level?

Because my cupric nitrate/ammonium chloride did so little on the dutch gold, I wonder if it goes bad over time. It has been mixed about 2 weeks. DJM states that the only common patination chemical that goes bad quickly is sulferated potash. Does it need to be hot to work? The first time I used it on copper at about 120*-130*. It worked well on the copper. Today I tried it on dutch gold at room temperature, and mostly nothing. DJM says that this is his favorite chemical on dutch gold. How long does it take to work?

Is there a finish I can put on the green blue patina that won't cause it to disappear?

Is this process totally unpredictable as to the results, or can I expect it to be reasonably consistent from piece to piece?

Sorry to ramble on, but I am hopping that somebody(s) out there has had some experience with these problems.

Thanks for the help.

[Dave Mueller]

Brian,
I took David's patination class and subsequently met with him several times at AAW and SWAT meetings. I have not had the problem of colors continuing to change after spraying with a topcoat, but have experienced the same problem you did with losing the blue/green colors when topcoating. I asked David and he confirmed that it happens, but suggested that using multiple thin coats of Krylon Crystal Clear Acrylic Coating 1303 may work. That seemed to help some, but did not eliminate the problem entirely.

I have not used copper much. I like dutch metal patinated with sodium sulfide (see the picture below of a sphere which had a lot of green that was lost when it was topcoated). Dale Gillaspy recently posted a vase using copper on http://www.sawmillcreek.org/showthre...-from-my-class that he did at David's class, so maybe he can weigh in on this thread.

I suspect that the colors result from interference in the thin oxide films formed by the acids. Since greens and blues are shorter wavelengths than red and yellow and therefor thinner films, the topcoat may overwhelm them. Although, this doesn't make a lot of sense, because the oxide films are probably submicron thickness and the topcoat is likely hundred of microns thick, however, it is the only explanation I can come up with.

Patinated Sphere - Stand.jpg

[Thom Sturgill]

Wish I knew more and my experience is very limited, but when I googled 'patination topcoat' I found a site 'metallicfinishes.com' that sells materials. At the bottom of the page they list a product they call 'ReactArrest' which is sprayed on the finish to neutralize the agent and then rinsed off. They also sell an Acrylic sealer to topcoat with.

No connection to the company, never tried their products. Just responding to the idea that you probably do need to neutralize the acid.

[Dale Gillaspy]

I'll see what I can add. I think the best way to neutralize the acids when you are done with the patination is to gently pat them dry with a paper towel. The chemicals can temporarily loosen the gilding size, so you don't want to rub. I'm a bit puzzled as to your patination times, though. In class, and in other patina's I have worked with, I have measured the exposure time in minutes, not days.

It sounds to me like your cupric nitrate solution is bad. It does last a little longer than the others, but I think a week or 2 is pushing it. I thinks when David talks about it going bad, he is measuring time in days, not weeks. If it doesn't smell, it is probably inert by now. A couple of days mixed is probably all you are going to get. Eventually, they can lose their potency even when dry, but that usually takes years. I use the Krylon topcoat mentioned above, and have not had the darkening problem to the extend you described. The blue/turquoise color will tend to dull a little, but not a lot.

As far as predictability, it is pretty black. What I mean by that is, you can predict what general colors a particular chemical will do to a certain metal, but beyond that, no so much. Factors such as time of exposure, concentration (Even though it seems like you are mixing the same every time, there are minute differences.) mineral content in the water, method of delivery, will all have an effect.

The last time I used the Cupric Nitrate mixture on Dutch gold, it took about 15 minutes to get the effect I was after.

[Brian Brown]

Thank you all for your comments. Dave, I really like your sphere. It has the look I am trying to get. Did you build up your layers with multiple applications of chemicals, or do you do just one application? Dale, your vase is beautiful. Was the leaf created with a stencil in friskit, or did you do it freehand?

I am looking forward to trying again. I'll have to get some fresh chemicals, and make sure that they are freshly mixed before applying them. I have one bowl that is ready for top coating, and another that is ready for patina over dutch gold. Then I'll try to get some pictures.

[Dale Gillaspy]

Brian, I didi those leaves by tracing real leaves on Friskit. I would do it a little differently next time, but it worked OK. The toughest part was where the vessel curves so much at the shoulder.

[Paul Gilbert]

Disclaimer - I have never tried to patinize anything. I am speaking strictly as an over the hill chemist.
What you are doing is creating copper compounds on the surface of the leaf. Temperature matters a lot. The speed of a chemical reaction doubles with a temp. rise of 18 degrees F. (10 C). So if you get a result at 72 and then raise the temp to 90, it will happen twice as fast. At 108 it is 4 times faster and at 126 you are up to speed 8.

Cupric Nitrate should be stable indefinitely. Ammonium Chloride probably not very long. A mixture of the two probably is not very stable.

When you use sodium sulfide you are trying to create Cupric Sulfide (blue). This compound is not very water soluble so a water rinse after the process would be appropriate. If you get Cupric Chloride (green) with your Ammonium Chloride treatment, this compound is very water soluble and should wash off in a water rinse. If you get black with sodium sulfide then you probably formed Cuprous sulfide which is insoluble. I might try to oxidize it up to the Cupric salt with a bit of hydrogen peroxide. A dilute solution of bleach might also work.

When you are playing around with chemicals be aware that sodium sulfide should never be mixed with an acid. You get hydrogen sulfide (H2S) which is a poison gas. It is the rotten egg smell. If you can smell it, you are OK, but in stronger concentrations it kills the nerves in you nose and shortly you will get a ride to the morgue.

[Dave Mueller]

I patinate outside whenever possible. That's what we did in David's class.

[Brian Brown]

Thanks Paul. This is great information. I was hoping a chemist would chime in. Most of the formulas for the solutions make large quantities, and for what I am doing, and with the short life span of the solutions, I like to mix them proportionately smaller. My biggest problem is finding a way to measure the chemicals in such small quantities. How long can I expect these solutions to last after mixing?

sodium sulfide
Barium Sulfide
Cupric Sulfate
Ferric Nitrate

Thanks again for all the great information.

[Paul Gilbert]

Brian - The solution to making small quantities is to use a scale that is accurate to 0.01 grams. These can be found in a number of places. I got mine at Harbor Freight for less than $20. I checked it with a good set of weights and it is dead on.

The compounds you listed should have a shelf life exceeding a couple of months providing the pH of the sulfides is slightly basic and the copper and iron are slightly acidic. The sulfides will give off H2S in an acid environment and the copper and iron will precipitate from solution in alkaline solution. You will see a visible flock if this happens. If you mix the sulfides with the copper and iron salts you will get an immediate precipitation.

[Dale Gillaspy]

If you slightly crush the dry chemical so it fits in a measuring spoon, add 1/4 teaspoon dry chemical to 1/2 cup warm water. That will give you a good amount to work with but not be wasteful.