Kinda Fishy Story

[Stephen]

bought a tsuba while back from a mate down under, he tossed in some extras, two kashira, thank you sir.

 

after playing around cleaning them of lacquer a LOS bath, they were bright brass. 

 

well they left a lot to be desired about. So into the fishtank they went. forgotten about for a few weeks until tank cleaning time.

 

Seems the ammonia from fish poo do a fair job of pantiating. 

 

FYI Wont work on copper.

 

[EdWolf]

Hi Stephen,

That turns out great. Good job.

Regards,

Ed

[christianmalterre]

so up from now one does "smell" you before one does sight you ?

 

second and agree...nice job here!

 

Christian

[Brian]

Not bad at all!
Do I need to get some fish now?

[vajo]

 

Sounds interesting Stephen. The hidden secrets of patination in ancient Japan. Now i know why the have koi 

[Hoshi]

Very nice. Can I send you a few for the same treatment? How much you charging ?   

[John A Stuart]

You could package the bottom sludge as Dr Fish's Patinination Compound and make some spare dosh. John

[Stephen]

Chris...has to be brass

[EdWolf]

It only works with brass because it contains zinc. The zinc part gives the brass the nice patina. Brass can range in color from red to yellow depending on the amount of zinc added to the alloy.

[Ken-Hawaii]

So feeding the fish different dosages of zinc supplements would change the patina colors, too, huh? 

 

Ken

 

[SAS]

Brilliant!

[Stephen]

a better explanation from Sensei

 

Probably not the poo so much as just oxygenated water. If there was any significant ammonia in the water the fish would be unwell I think. Ammonia, and salt, tends to promote the development of various copper salts which give us the common green/blue types of 'copper rust'. 

With your pieces I suspect the colour is coming almost entirely from cuprite (Cu2O, basically 2 copper atoms binding with one oxygen atom) which is red. Other alloy components, like zinc in this case, can become oxides of themselves, zinc oxide is white, and thereby serve to alter the red colour we see from the cuprite. There might be some traces of sulphides present which would also further modify the colour we 'see'. Copper alloys are not perfect mixtures, more like a cake with raisins in it. You can imagine a field of red cuprite with spots of white zinc oxide scattered about. We perceive a colour as one tone but it's a bitlike a TV image in that it's made up of only three colours, red, green and blue. 

A further 'modifier' to the wavelengths of light reflecting off the patina surface is the actual physical structure of that patina layer. Not so much the mechanical polish, although that is a part of it, but more the speed and time scale at which the patna grew. This effects the surface structure which in turn effect how light behaves when it hits it and is reflected. Less 'artfully' created patina can often have a 'stain' like layer form which inhibits further patina grows and leaves a slight translucent interference layer instead. This can look a bit like petrol/or gas on water.

It's obviously much more involved so I'm just trying to describe what's going on as simply as possible.

Hope some of the above helps. Feel free to quote me :-)

regards

 

fh

[SAS]

While we have Sensei's attention, i would like to ask about the forming characteristics of brass; it has been my sense that brass is brittle....if true, how were the kashira formed? Is its malleability based on thickness or alloy?

[Ford Hallam]

Hi Steve

 

There are some brass alloys that are brittle but on the whole simple brasses with from 5% (gilding metal) to 37% (commercial brass CZ108) are all capable of being extensively worked. The correct annealing procedure is of course essential. Japanese brasses (shinchu) as found in tosogu range from around 10/15% to over 30% zinc. Edo period shinchu alloys invariably also contain traces of lead up to 1%. We expect to find traces of lead in the copper as a result to the refining processes that were used but those are typically less than 0.5%. Higher concentrations of lead might indicate a deliberate addition. Lead present at these low levels don't appear to reduce malleability but can play a part of developing a deeper patina tone. One of the shinchu alloys I make and use contains 15% zinc and .05% lead. I've drawn this alloy down to 0.5mm diameter wire quite easily.

 

hope that explains a bit.

 

fh

[SAS]

Thank you very much for your reply, Ford Sensei; this is an interesting area  that i will have to delve into in the future.