Silvering brass

I saw a bit of 'The Repair Shop' on TV recently and there was a guy who silvered a bit of brass (a strangely shaped miniature sword) by wiping some blackish sort of gunk on it. Frustratingly they didn't tell us what it was - Beeb policy I suppose. I also saw one where  a 'special wax' was used to finish a woodworking project. The label on the container was (in)conveniently turned away from the camera. Back in the day we all knew what they meant by 'sticky-back plastic'!

I haven't any pressing need to silver brass, but it interested me and I had a look round. It seems that horologists use a paste of silver chloride and potassium hydrogen tartrate to restore clock faces. Presumably the tartrate ions form a complex with the silver which brings it into solution enough to react with the copper in the brass? I haven't found out what the black gunk is though!

Does anyone have experience in this area? Although not pressing I sometimes make things from brass and adding a bit of of silvery bling might be - well - entertaining.

Robin

Edited By Robin Graham on 11/05/2019 23:05:35

The wax was Rennaissance Wax - otherwise known as Renwax.

Very useful stuff.

Thanks - I've heard of it but never tried. I shall get some.

Robin

Dial silvering is demonstrated here: **LINK**

https://m.youtube.com/watch?v=F1JxGUgcHnE

It's a very simple process ... just need to maintain cleanliness

MichaelG.

For Silver Plating without electricity there is this stuff, I’ve used it to repair the plating on old items but think it does list plating brass etc on the label.

HS Walsh

Edited By V8Eng on 11/05/2019 23:13:15

How on earth does that work then V8Eng, sounds like snake oil (only sounds like, your results sound pretty convincing)

Renwax can make brass go silver?

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That word "also" is important

I'm pretty sure that Robin doesn't expect Renaissance Wax to silver his brass.

MichaelG.

'How on earth does that work then V8Eng, sounds like snake oil (only sounds like, your results sound pretty convincing)'

The chemistry is simple enough. Copper (and Zinc) are both more reactive than Silver, so when Brass comes into contact with a Silver Salt, they exchange ions. A layer of Silver deposits on the Brass in exchange for a Copper Salt that can be washed off. Not Snake Oil but the Silver layer produced is very thin. Better for repairs and touching up than new work.

In the same way acidified Copper Sulphate solution leaves a thin layer of Copper on a steel plate because Iron is more reactive than Copper. Before Marking Blue, widely used for scribing lines on ironwork.

Although there's enough energy in the above reactions for them to occur in solution the results may be disappointing. Silver works quite well but the Copper Sulphate reaction leaves Copper so loosely bonded to steel it can be wiped off with a cloth. Electroplating applies energy to attach metal films firmly and in much thicker and less spongy layers. Although simple in principle the chemistry needed to get consistently good results from electro plating is tricky; it's hard to do well at home.

Dave

Edited By SillyOldDuffer on 12/05/2019 10:37:34

It's a two stage process. You can find the powders on Ebay.

https://www.ebay.co.uk/itm/Professional-Silvering-Powder-Trade-small-200g-PLUS-200g-Finishing-Powder/323775594134?hash=item4b62877e96:g:lrYAAOSwNSxVBpzY&frcectupt=true

I have used this type of product for silvering a brass clock dial and bezel which can be seen in my album. The most important part of the process is cleaning.

Russell

Rennaissance Wax is only a protective finish mainly for wood. Extensively used by the british museums as a protector it also halp to keep fingerprints off of things that need to be protected and are handled.

And yes it does work I have used it on many occassions the stuff I got is expensive being over £10 for 65ml

It can be used on furniture,leather, paintings, metals, marble ivory and then some more

Edited By Derek Lane 2 on 12/05/2019 12:46:01

+1 for Dave Lane, I use renaissance for protecting the non stainless blades of my miniature knives. Use it very sparingly, little and often to build up an invisible layer.

Stops brass and nickel tarnishing after polishing too.

Best regards Mick

Thanks for replies. As MichaelG cannily perceived I didn't think Renwax would silver brass - it was a subsidiary question born from old man grumpiness about the Repair Shop programme. It's heartwarming to see heirlooms restored, but frustrating when we don't get to see the nitty-gritty. It just annoys me.

Armed with info from here I might just make my own version of Renwax . I have a chunk of micro crystalline wax.

Dave - I understand the basic chemistry of the process, but I wondered about the use of silver chloride, which is pretty much insoluble in water, as the source of silver ions. Why not use a soluble salt such as silver nitrate?

Robin.

Sorry if I accidentally taught granny to suck eggs!

I wondered about Silver Chloride rather than Silver Nitrate too. There must be a reason for it. I have a copy of "Dr Ure's Dictionary of Arts, Manufactures and Mines" (1875), which describes how to silver mechanically (a rubbing on process like Gold Leaf), and chemically. The chemical process starts by making Silver Chloride from Silver Nitrate by adding Common Salt!

Pearlash is Potassium Carbonate, and Whiting is powdered chalk (Calcium Carbonate).

Possibly the silvering process is improved by rubbing the surface with a mix of mild abrasives, with the Chloride only reacting during the stir? This is a guess based on Sliver Chloride being insoluble in water, but somewhat soluble in an alkaline solution, whereas Silver Nitrate is very soluble. The need to rub might allow the operator to control the layer, whereas Silver Nitrate would be uncontrollable. Whatever is going on it's not as simple as O-Level Chemistry would suggest.

Dave

No need to apologise for the egg sucking tutorial Dave - it happens that I have a background in chemistry/physics, but there will be people who light on this topic from internet searching and benefit from your explanation.

Dr Ure's opus looks rather wonderful! Do you have the original (C19) volumes? They seem to be quite rare - I had a look round (I'd not heard of the work before) and it seems I can get a 1999 Routledge reprint from Amazon for a bit under $2000!

Returning to silver chloride, I reckon you're right that it's about controlled deposition. Tartrate ions will complex the silver from the chloride and, after further research, it seems that excess chloride will do the same job.

I'm intrigued by the inferior buttons. Corrosive sublimate is mercury(II) chloride I think, so mixing that up with the silver and zinc sulphate is going to make some sort of amalgam possibly.

Robin.

Edited By Robin Graham on 14/05/2019 00:17:45

Edited By Robin Graham on 14/05/2019 00:18:17

Edited By Robin Graham on 14/05/2019 00:36:45

I was intrigued by one company who sell silvering powder made to an old family recipe from real antique silver. I found this page that explains Displacement plating

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Very interesting, Adrian

Thanks for the link.

MichaelG.

Can anyone shed light on a process I vaguely recall for crack testing Brass Cartridge cases. Cases were either dipped or rubbed over with "snake oil " that turned them silver except where there was a crack ( from the deep drawing process) that appeared as an uncoated line. Rejected of course!

I seem to remember that mercury was involved so the whole process will be considered "iffy" today.

Bob D

This is essentially the same as Fox Talbot's original process for making photographic prints. Soak paper in salt solution and then coat in silver nitrate (or float in a dish of the same) to make Silver Chloride 'in situ'

Its really quite an elegant solution. As Silver Chloride is insoluble in water create it from salt and silver nitrate to give sodium nitrate, which is soluble, and washes off, as the other product.

Albumen printing paper was made in a similar fashion only the albumen (egg white) with salt added was spread on the paper which when dried gave a gloss(ish) finish. The paper was similarly sensitised as above in silver nitrate before use.

To think that through is a true spark of genius!

Edited By Nick Clarke 3 on 14/05/2019 19:25:51

A long time ago (1964ish?) I worked in the QC lab of a non-ferrous metals foundry. One of my duties was to polish brass and bronze samples for microscopic examination of grain structure. After polishing we painted the surface with an acidic solution of mercury(II) nitrate which we prepared ourselves by dissolving metallic mercury in concentrated nitric acid. Mercury deposited on the polished surface and formed a silvery amalgam which revealed the grain structure. I always assumed that residual nitric acid in the brew preferentially etched the grain boundaries and the silvery amalgam gave contrast, but maybe the deposition/amalgamation process was also sensitive to grain boundaries. Same process I guess.

Robin