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Rokusho palette and processes


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Being fairly new to irogane and rokusho patination, I'm trying to get some understanding of the basic color palette that is available to me when planning a composition. Although I have been able to find some good information here and on other sites, I was hoping that people with more experience could fill in some of the gaps in my understanding (or correct it if it is wrong!).

I only have (limited) experience with copper, 20/80 shibuichi, fine silver and 24k gold. My current notes have the following:

- Copper will shift color from orange to brown and eventually to red given enough time (~8/10h). I have gotten good orange with as little as 30m, and a (still orange-ish but) decent brown after 1h. I have not chased after the elusive red just yet.

- Shibuichi will give light grey to dark grey depending on copper/silver ratio, and takes about 25/30m. I have only used 20% silver so far, and gotten quite a dark shade. My understanding is that increasing the silver content yields a lighter color. In addition, Jim Kelso details here a process of silver enrichment, which can achieve gradients between light and dark areas on shibuichi.

- Fine silver will not change color, but may develop a yellow film on the surface after some time. A pinch of alum can help avoid this according to some sources, though I have at least once seen this film form regardless (as I said, I'm new at this, and so is my copper pot!)

- 24K gold will not change color, I do not know about lower karat.

- Shakudo (no personal experience) will go black with a deep purple hue at around 1h.

I have found little information about rokusho on brass or bronze. I plan on experimenting some (including non-traditional alloys such as nickel-silver), but an idea of what to expect would be useful as a point of comparison. I have heard that one should use a separate niage batch to patinate brass, but I have not heard why (I imagine this is due to the Zn and also applies to other Zn-containing alloys, but I don't know what that actually does to the solution and why it should be a separate batch). In addition, this would seem to preclude patinating a multi-alloy piece (say, shibuichi + copper + brass); is this simply not done?

I'm also quite intrigued by the silver enrichment process for shibuichi, though it's unclear to me how the enriched layer is preserved given that the patination process begins with polishing the entire piece (abrasive powders, and/or charcoal). I am guessing that the polishing step can leave enough of the enriched layer alone to still achieve the desired result, and that experience teaches how deep that layer goes for a given amount of heating/pickling cycles (and I suppose for a given silver/copper ratio). I'm also wondering if a similar process can be used on other copper alloys: if oxidation mostly affects copper, then brass/bronze, and even shakudo may also be affected in a similar way, perhaps yielding useful color gradients?

Finally, am I missing some of the basic colors in the palette? For instance, I really really wish I could achieve some form of green (i believe I could with different chemicals than rokusho, but combining that with rokusho-based colors would seem extremely challenging if not downright impossible)

Any information/correction on any of the above would be immensely appreciated.

Cheers!

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A lot to cover here Francis, but you clearly  have a good grasp of the basics to ask such good questions. Experience is the key to all. You will hear various truisms, some which will bear out and some which won’t. Also something that works one time may be hard to replicate. Small things that you didn’t notice may have an effect. It’s easy to understand why the Japanese had specialists who only did patina, or it was their primary focus in a studio. I struggled with a certain piece, finally getting it acceptable without knowing quite why. I took it to Japan and consulted with a professor at Tokyo Geidai (U of Fine Arts) and he said very clearly what was going on and the light-bulb went on. I had done the right thing, finally, but without really grokking why. The point is, again, experience is the key. I would focus on smallish works, as you are, and combinations of colors, and move on with what you learn. I have found that some pieces I considered small tests turned out to hold up quite well as finished pieces.

some specifics to follow....

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Thank you Jim, so much to learn and I should probably pace myself a little bit :) 

On 6/14/2021 at 9:07 AM, Jim Kelso said:

I would focus on smallish works, as you are, and combinations of colors, and move on with what you learn

Agreed. For the piece I am working on now, I am combining what I've used in the past with shibuichi 40/60, which I haven't used before. It's one thing to think "light gray" and "dark grey", but it will be interesting to have a piece that actually shows them both in contrast to each other, and to silver.

I should be able to do some patination tests this weekend on a number of additional alloys, I'll report my "findings" here. Perhaps this thread can continue to capture more of my notes in the future, as well as comments from anyone else who's knowledgeable and/or interested.

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I did some tests today with several different alloys in an old solution (used on 3 previous occasions, initially 4g rokusho, 4g copper sulfate, a pinch of borax and one of alum). The pieces were:

- 260 Brass: 70% Cu + 30% Zn
- 230 Brass ("NuGold"): 85% Cu + 15% Zn
- Nickel silver: 60% Cu, 20% Ni, 20% Zn
- C145 copper: 99.4% Cu, 0.01% P, 0.6% Te

...as well as what was probably a mistake, which I only realized after the fact:

- 954 Bronze: 86% Cu, 10% Al, 4% Fe (!)

I didn't realize the bronze I had was aluminum bronze, which contains iron, known to ruin the niage bath. I had not planned to reuse the solution for anything after that, but it's likely to have changed the effect on the other alloys, rendering this whole test dubious.

This is still an experiment I suppose, so for the record, here were the results:

GfjFACS.jpg

From left to right: 

- copper got substantially darker in 1h than in my previous experience, and has a *very slight* blueish tinge when viewed in the shade

- 230 brass immediately went blue/grey, and shifted to nutty brown in about 20m with little change after that (just a bit more saturation)

- nickel silver was similar to 230 brass for a good while, but ended up somewhat reinforcing its blue tinge over time, resulting in a brown that tends toward bordeaux (quite pronounced when viewed in the shade).

- 260 brass went from yellow to orange, with a really satisfying tone at about 30/40m, then slowly got darker and closer to 230 brass, only slightly more redish.

- 954 bronze did its own thing: it was entirely unaffected by the first 20m and then developed a yellow/orange color. Though the blotchiness is likely my fault for not polishing well enough, i suspect the "bubbles" are casting defects.

It's pretty much impossible to take a photo that accurately portrays the colors the eye sees under different conditions, so here's another one with different shades while the pieces were still in the cooling water bath:

q62WTwW.jpg

For reference, here are the unpatinated alloys:

5NPnln6.jpg

I'll be trying some of these again in a more controlled run (new niage bath, no iron, and C110 copper instead of C145 for a better baseline). It'll be interesting to see the difference when iron isn't added to the mix :P 

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That's a very interesting test Francis. It may be that the low percentage of iron had little, if any effect. There are so many variables in the niage process. I applaud all efforts toward gaining depth of experience. It's interesting how the wet alloys look so much richer. It is true that lighting makes huge differences in how these colors look. I try almost always to use fresh solution, but this is costly, and my lack of experience using used solutions does not inform how long, and under what conditions, a solution remains viable.

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