Matsunoki Posted January 31 Report Posted January 31 Another thread on here has been talking about brass type alloys and their appearance/patina. That discussion reminded me of this tsuba that has returned to me having had a short holiday elsewhere🙂 One side has been exposed to the light/atmosphere, the other side shrouded. It looks like it was hung via a very thin thread rather than boxed. The difference is quite spectacular, you would not believe they are sides of the same tsuba made from the same alloy. Anyone beat that for a stark contrast? 5 1 Quote
vajo Posted January 31 Report Posted January 31 Maybe the ura side got an extra treatment with niage? Quote
Matsunoki Posted January 31 Author Report Posted January 31 Just now, vajo said: Maybe the ura side got an extra treatment with niage? Don’t think so. Quote
Hokke Posted February 1 Report Posted February 1 17 hours ago, vajo said: Maybe the ura side got an extra treatment with niage? the exposure to oxygen is likely the cause as Colin alluded to. Exposure to open air in a humid environment will accelerate the reaction converting brass to brass oxide. Interestingly enough, the oxide layer serves a purpose by making the base metal more resistant to chemical reaction. Quote
ROKUJURO Posted February 1 Report Posted February 1 Calabrese, as brass is an alloy, there is no "brass oxide". If the different colouring was caused by oxygen, why would it only affect one side? I could imagine that this is not brass but SHIBUICHI with a SHAKUDO content (called KURO SHIBUICHI) which makes it react to light as Colin suspected. There are also TSUBA with different alloys on the faces but that would often show on the MIMI. Quote
Hokke Posted February 2 Report Posted February 2 1 hour ago, ROKUJURO said: Calabrese, as brass is an alloy, there is no "brass oxide". If the different colouring was caused by oxygen, why would it only affect one side? I could imagine that this is not brass but SHIBUICHI with a SHAKUDO content (called KURO SHIBUICHI) which makes it react to light as Colin suspected. There are also TSUBA with different alloys on the faces but that would often show on the MIMI. Jean, it would only affect one side because only one side was "exposed" to open air. If the tsuba was in a lined box as many are, the side facing up would oxidize far more quickly than the side facing down. Light has little to no effect unless it is direct sunlight causing an increase in temperature in combination with a more humid environment. I am very interested to hear why you believe brass and other alloys cannot oxidize though. Quote
Matsunoki Posted February 2 Author Report Posted February 2 8 hours ago, ROKUJURO said: I could imagine that this is not brass but SHIBUICHI with a SHAKUDO content Jean, this is definitely not anything to do with shibuichi or shakudo. It is definitely sentoku ie a brass type alloy and that definitely does develop an oxidised patina depending on what it is exposed to. I’ve handled a fair bit of Japanese mixed metalwork and its restoration. The re-patination of overcleaned pieces basically restores a fine layer of oxides on all/any alloys - the final colour of which will vary depending on the actual balance of constituent metals used and the chemicals used in the process. That is what gives the often stunning multicoloured effect found on these pieces. Gold however does not oxidise (I think!) On this tsuba, if you look closely on the front side you can see a very fine line that goes from the nakago ana vertically to the rim. That strongly suggests it has been hung up to display using a fine wire or thread. Thus the face will have been totally exposed to whatever whilst the reverse will have been protected. I first bought this tsuba together with a few other really good Kinko pieces all of which had the same vertical line. I suspect that some of the colouration could also be nicotine…..maybe on the wall in a “gentleman’s study” type environment. 2 Quote
vajo Posted February 2 Report Posted February 2 The side is longer treated with niage. There is no mystery in making one side darker. Quote
Matsunoki Posted February 2 Author Report Posted February 2 Sorry Chris, in this instance you are wrong. I have the benefit of handling the piece and also the others that came with it. All had similar heavy discolouration to one side. 1 Quote
Matsunoki Posted February 2 Author Report Posted February 2 Here is another from the same group that I bought. It has the same heavy patina on one side and a similar vertical hanging mark This has nothing to do with a heavier patina being applied to just one side. 5 Quote
ROKUJURO Posted February 2 Report Posted February 2 Calabrese, soft metal alloys do not react exactly like their components. You cannot have "brass oxide" (or "steel oxide", for that matter), and the copper content will not react as if it was present as single metal. The same applies for the zinc in this alloy. Brass is a rather non-corrosive alloy, even under salt-water conditions. This is not the case for copper or zinc as such. As the TSUBA was possibly suspended as shown by Colin, I think I can keep my opinion up that not oxygen alone was the cause of the darker colour on one side. As far as I know, SHAKUDO darkens under the influence of UV light, so my assumption the TSUBA might have been made of KURO SHIBUICHI. As Colin has seen the TSUBA in hand, he can give a better guess what it actually is made from. I would like to mention that sulphuric gases (H2S and SO2) have a strong darkening effect on brass. However, a freely suspended TSUBA would show this effect on both sides. The colours (= patina) that can form on brass are mostly caused by sulphides, not oxides. Gold (platinum, palladium) does indeed not react with oxygen. Quote
Alex A Posted February 2 Report Posted February 2 The Complete Guide to Brass Oxidation: Causes, Prevention, and Cleaning - MFG Shop Imagine the tsuba hanging in some room with varying temps etc, sulphur from coal fires etc. No surprise to me you will see tsuba with differing patina, especially if sat on a wall or whatever 2 Quote
ROKUJURO Posted February 2 Report Posted February 2 2 hours ago, Matsunoki said: I suspect that some of the colouration could also be nicotine…..maybe on the wall in a “gentleman’s study” type environment. Hi Colin, of course the TSUBA might have been hung on a wall and not freely. This would then explain the one-sided colour. Nicotine is an almost colourless liquid. What we see as brownish residue in smokers' rooms is tar. In case this settles on a TSUBA, you could easily wipe it off with a solvent agent. Quote
Matsunoki Posted February 2 Author Report Posted February 2 Thanks Alex. Boy we are making hard work of something blindingly obvious🙂 1 1 Quote
Alex A Posted February 2 Report Posted February 2 The dark patina is what i want for the brass cannon, when i eventually get around to it Colin. Seen some firm online that makes a product that will achieve that colour. This is an old cheap cannon ornament, i am not recommending this for tsuba, at all. But yes, thanks Colin, thats what I'm after and good to see the variation. On a level with antique bronze or thereabouts. Quote
ROKUJURO Posted February 2 Report Posted February 2 Alex, just expose it to the fumes of liver of sulfur (H2S), it works immediately. 1 Quote
Alex A Posted February 2 Report Posted February 2 Ive been told and read about that Jean, but not sure it will end up dark enough. Though will defo look into it more and maybe do some tests to find out. Cheers. Quote
vajo Posted February 2 Report Posted February 2 52 minutes ago, Matsunoki said: Sorry Chris, in this instance you are wrong. I have the benefit of handling the piece and also the others that came with it. All had similar heavy discolouration to one side. Colin i think i misunderstood you, sorry. I thought these doubled color tsuba was the work of the artist. No i understand it was obvious the reason of a long time presenting. 1 Quote
Gunome Posted February 3 Report Posted February 3 On 2/2/2025 at 11:28 AM, ROKUJURO said: As far as I know, SHAKUDO darkens under the influence of UV light I have never heard of this. Do you know if it would work to repatinate a shakudo insert on an iron tsuba by exposing it to the sun? how long would it take? sorry for the off-topic Quote
Matsunoki Posted February 3 Author Report Posted February 3 35 minutes ago, Gunome said: Do you know if it would work to repatinate a shakudo insert on an iron tsuba by exposing it to the sun? how long would it take? I am not 100% sure but I was told by Ford (so really I should be 100% sure!) that “old” shakudo will repatinate itself if left in the atmosphere (but kept dry). What constitutes old shakudo again I’m not sure but I would have a reasoned guess at pre-Meiji. How long it takes….no idea, never had to try it. I’d also guess it must be perfectly clean to achieve an even result. Good luck! Quote
Franco D Posted February 3 Report Posted February 3 1 hour ago, Matsunoki said: I am not 100% sure but I was told by Ford (so really I should be 100% sure!) that “old” shakudo will repatinate itself if left in the atmosphere (but kept dry). What constitutes old shakudo again I’m not sure but I would have a reasoned guess at pre-Meiji. How long it takes….no idea, never had to try it. I’d also guess it must be perfectly clean to achieve an even result. Good luck! High quality shakudo will repatinate itself given time. The lower the quality of the shakudo the greater the chance it will not recover back to where it was originally. In fact, even chemical inducement may end in disappointment. Good quality shakudo when repatinated will not only take but will continue to become richer in the depth of color and be evenly distributed. One of the keys to a properly restored piece is that the restoration cannot be detected even by sharp eyes, "doesn't look new." 1 1 Quote
ROKUJURO Posted February 3 Report Posted February 3 After re-reading about re-patinating SHAKUDO, I am no longer sure what causes the "self-healing" of the blue-black colour. It may well be the atmosphere or a combination of light and air. For those interested, there is a lot to read about it in the i-net. Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.