Kin-furubi patination

Sandra Wilson 2024 - Pendant Piece, 950 Silver with Kin-furubi patination in engraved surface 45mm x 40 mm x 1mm.

When reading Eitoku Sugimori’s book on Japanese Patinas (2000) - my interest was piqued by a metal patination recipe called kin-furubi. Translated, Kin means gold and furubi means to be old and faded/ time-worn so this is a patination recipe to age metal. In Sugimori’s book he suggests the traditional kin-furubi recipe involves a mixture of pure gold and aqua regia, a potent acid that dissolves the gold. Aqua regia however is a very dangerous chemical and not one I would be interested in working with. Sugimori however also suggests a safer alternative that utilises a gold plating solution mixed with alcohol. Unfortunately this recipe is not very precise and despite speaking to two different plating suppliers in the UK I could not find a solution that I believed could work. As my practice of working with precious metals recovered from electronic waste has become more chemical in nature I was curious as to whether kin-furubi could be a patination recipe that could utilise gold in solution from e-waste.

During my time in Japan last October I was introduced at the Aokin school to Kenji Io the father of Japanese silversmith Koichi Io. Around 25 years ago Kenji co-authored a book on Metalwork Colouring Techniques (see below). The book included valuable information on kin-furubi. The book is in Japanese however google translate was able to provide what I believe is a reasonably good interpretation of the page I was interested in. The recipe described dissolving 1 gram of gold in 7.5cc of nitric acid and 7cc of hydrochloric acid (aqua regia) to make gold chloride. Add the gold chloride to a solution of 250cc of ethanol and finally add a tincture of iodine.

I am fortunate to have research collaborators at Edinburgh University chemistry department who I could get advice and guidance on how to prepare the solution back here in the UK. A UoE postdoctoral research assistant was happy to assist me in preparing the solution. Their advice was to start with a pre-prepared gold chloride powder to which we could add the ethanol and tincture of iodine. In chemistry a tincture of iodine is typically 25 - 60% concentrate in alcohol usually ethanol.

In the lab we created two solutions - a weak solution that had less than 1g of gold concetrate and only 20 - 30mg iodine. The strong solution had 1g gold concentrate and 50mg iodine. The weaker solution appears to create more brown shades and the stronger solution darker greys and blacks. I kept both solutions in brown glass bottles which block out UV light. I experimented with 950 silver and sterling silver.

Kin-furubi can be applied with a paintbrush or cotton bud to a clean metal surface. The dark effect on the metal is quite instant and so could also be used to paint brush strokes onto metal. Before applying kin-furubi clean the silver with a paste of baking soda. Let the object dry preferably in direct sunlight but you can also use a UV nail light box to dry. Apply the kin-furubi solution - when the piece turns black, rinse in running water and rub with a paste of baking soda until the desired effect is reached. You can also use fine steel wool to remove the patination from higher areas, as I did in the pendant piece at the top of this post.

Its important to remember that this patination solution only works on silver and not on copper.

The final stage is to seal with wax - either renaissance wax or as in Japan, ibota wax that is derived from the secretions of an insect. I bought some of the ibota wax in granules that can be heated in a small muslin parcel and smeared across the metal to seal. Wait at least 24 hours before sealing to ensure the work is completely dry.

Mariko Sumioka from the Aokin school suggested to me that Kin-furubi is a stronger longer lasting patination than liver of sulphur and the effect is not so harsh, not so dark. This solution therefore provides both chemical protection and aesthetic interest. Importantly for my research, gold chloride which is an output from the hydro-metallurgy process of recovering precious metals from electronic waste can be utilised in creating this patination solution. So a kin-furubi patination solution could have not only aesthetic and protective value but also contribute to a responsible making practice.

With thanks to the Aokin School, Mariko Sumioka, Kenji Io and Edinburgh University Chemistry Department. Special thanks to the Daiwa Foundation who supported this research in Japan.

Nunome Zogan

Gold is included on the European Chemical Society’s Endangered Elements list (2019). Gold is considered of “limited availability with a future risk to supply”. Gold, although found in many localities in Japan was never abundant. Japan’s frequent sumptuary laws also meant that gold was always a metal to be used sparingly. Consequently, Japanese metalsmiths developed various techniques that use a minimal amount of gold for maximum effect. These techniques include creating gold alloys (eg. Shakudo 95% copper 5% Gold), depletion gilding (bringing the gold to the surface) and different types of overlay and inlay that use thin gold foils (eg. 0.02mm thick).

Nunome Zogan means cloth weave overlay and uses very thin foils - 0.02mm thick and the gold is attached to the base metal by creating a cross-hatched ground made with chisels. Around 7 - 9 chisel marks per mm created in three different directions at 45 degrees to each other. The technique is a type of Damascening that was introduced to Japan by the Portuguese in the 16th Century.

The technique was originally used on Iron and Steel to decorate weapons although more recent practitioners have expanded this to include copper, brass and sterling silver. I have been experimenting with this technique on sterling silver. It is a difficult technique to master as very little information is available. This is perhaps in part due to the Japanese teaching philosophy which encourages the student to discover for themselves what works as part of their education. I am particularly interested to see if the gold recovered from electronic waste can be rolled into thin foils and used in this frugal technique.

Candelabrum Repair

I’m a big fan of the BBC TV programme ‘The Repair Shop’ that restores to their former glory people’s precious family heirlooms that have fallen into disrepair. I prefer it to ‘The Antiques Roadshow’ which tends to focus on the monetary value of heirlooms. In contrast, The Repair Shop is concerned with the emotional value of the objects and the connection they provide to lost loved ones.  So last year when I was given the opportunity to restore something belonging to my University of Dundee family, I was excited and nervous in equal measure. The University of Dundee Museum Services has the responsibility of looking after the University’s silver collection and Matthew Jarron, Museum Collections Curator, approached me to ask if a piece could be repaired. The piece that had become broken was a candelabrum, described in the catalogue as a ‘branched candelabra with five candle sockets in bowl’ (sic) made in 1957. The dimensions of the candelabrum are 32.5 x 24x 35.5cm so it’s a sizeable work – the biggest I’ve ever had to work on. In researching this blog post I also discovered that the candelabrum is one of two belonging to the University.

The candelabrum had been designed and made by English silversmith Leslie Durbin (1913 – 2005) who trained under Omar Ramsden. During a period of the growth of universities his business did well from a number of commissions for ceremonial silverware. Durbin is perhaps best known for his work on the ‘Sword of Stalingrad’. The sword was presented to Joseph Stalin in 1943 by Winston Churchill as a homage from the British people to the Soviet defenders of the city in the Battle of Stalingrad. We know the candelabrum is by Durbin because of the hallmarks on the silver. Hallmarking has been around for over 700 years and determines the quality of the metal, the maker’s mark and the year the work was made.

In this case the stem of the candelabrum had fallen through the base – cutting straight through - perhaps from the weight of the candle sockets themselves or more likely from a weight being placed on top of the stem. There were also several dents in the base that needed to be hammered out.

Hammering out the dents in the base of the work was tricky as I had to find a steel stake roughly the same curve as the base. I have a series of radius gauges that that I learned how to make and use in silversmith Adrian Hope’s workshop. These are differently angled curves, so I could place one of these over the curve of the base and then use it to try and find the same curve in a corresponding stake. A profile gauge also performs the same function. Gentle tapping with a planishing hammer slowly removed the worst of the dents. The real challenge was to determine how best to reconnect the stem to the base. I could just hard solder the two pieces back together again – however I was unsure if this would create the secure connection that I was looking for. I decided to add a silver disc between the two sections. The bottom of the stem was soldered to the disc and the disc was attached to the base effectively creating a shoulder for the stem and strengthening this central area.  

You can learn a great deal from studying the work of another silversmith. For example, I was surprised at the thickness of the silver sheet that he was working with - over 1mm thick in places - making this candelabrum a robust and sturdy item for the table. The wire soldered around the outside edge was something that was very fashionable around the time it was made but is not something that we teach now, partly because this skill has been lost. Rod Kelly is a Scottish silversmith based in Shetland who has recently documented on Instagram the process for attaching a wire to a large plate. This is a process that takes hours of painstaking work, attaching and then hammering out the warping created from the work being heated. Another challenge encountered in this repair was trying to polish the hammer marks made from taking out the dents. The polishing machine in our workshop was not quite big enough, and we do not have a pickling pot big enough to take the work!

I hope that the repair I have made is an elegant solution, as the disc also echoes the wire soldered around the outside edge of the base. The disc is also an addition to the work, a little piece of me. This is akin to the Japanese art of repairing objects – Kintsugi - that treats the repair as part of the history of the object and doesn’t try to disguise it. Now that the candelabrum is repaired it has returned to being used at the table for University dinners and ceremonial occasions and will hopefully continue to serve for at least another 60 years.