The following discussion about silver plating took place in the Moon-Net reflector. I found the subject so interesting that I decided to put together all the messages in this page.
On 12-Nov-2002 VK2KU wrote:
Does anybody know where to get silver plating solution in the US?
I am talking about the stuff that you rub on copper, not the electrolytic process.
I have seen a few sources in the UK (they call it liquid silver), but none so far in the US. Bringing that stuff from overseas can be problematic due to its hazardous nature.
On 12-Nov-2002 K4EME wrote:
Hi Marc, I used Cool Amp to Silver plate my Stripline LNA a few years ago. http://www.cool-amp.com/cool-amp.htm I hope this helps.
On 12-Nov-2002 WA4OYH wrote:
On 13-Nov-2002 K1FO wrote:
Be aware that Cool-Amp puts on a very, very thin crystalline coating of silver. It does not matter how much Cool-Amp you try to apply, or how hard you rub, it attaches via a chemical reaction to the copper or brass you apply it to and will not build up on itself. Even if you could make the Cool-Amp thicker it would not improve RF resistance as its crystalline structure has lower conductivity than "real" electroplated silver or copper.
It WILL NOT do anything to improve the RF conductivity of clean brass or copper.
This is not to say that Cool-Amp has no benefit. It offers some level of oxidation protection to bare copper or brass, that is it will slow down the decay of their surface conductivity due to oxidation. This is actually the objective of Cool-Amp. That is to keep copper oxide off switch contacts allowing them to maintain a lower contact resistance over time.
On 13-Nov-2002 G3SEK wrote:
There are several formulations for rub-on silver plating. It's true that these rub-on coatings will not build up on themselves, but an additional problem with gritty powder formulations is that they are grinding off the silver coating as you try to rub it on.
There is another product available in Germany, called "Anreibe Silber" (Rub-on Silver) which is a suspension of a soft powder in liquid. That gives a better coating than the gritty types, but you're still limited by the fact that it will not build up on itself.
However, you can also use this stuff in electroplating mode, and then it will build up a much thicker film.
There was an article in Ham Radio several years back, by K9-somebody, about electroplating using spent photographic fixer - which is actually a solution of silver salts dissolved out of the film. The really neat trick was you don't need a bucketful of plating solution, big enough to immerse the metalwork to be plated. Instead the metalwork is kept dry, and you apply the solution in small amounts using a 'magic wand' - a carbon-rod anode with a small sponge fixed on the end. This is much more economical with the silver-bearing chemicals, and a real breakthrough for home electroplating.
The 'magic wand' anode is connected to the positive of a 30mA low-voltage supply, and the metal to be plated is connected to the negative. Then you dip the sponge into the plating solution and wipe it slowly onto the metal. The longer you stay in one place, the thicker the film that builds up. Pretty soon you've plated out all the silver from the solution, so you dip the sponge again and carry on.
This technique works fine with Anreibe-Silber. I used it on the baluns for the EME system, because they have to live outside, and also on many smaller items. Unfortunately none of these amateur techniques will plate over tin/lead solder - for that you need an 'industrial' plating process.
Can any of you German guys confirm whether Anreibe-Silber is still available? I bought some at Weinheim several years ago, but haven't seen it there in recent years.
The bad news is that this product is a cyanide formulation. The cyanide is locked up in the solid powder, so it's much less toxic than the solutions that professional electroplaters use, and it also comes with detailed product safety information. But I still wouldn't recommend it to anyone who doesn't have chemistry lab training.
If even the word "cyanide" scares you, then you don't have the training to use this stuff. And even if you can still buy it in Germany, your chances of importing it legally into the USA are probably zero.
The photographic-fixer method is still worth investigating, though.
On 13-Nov-2002 GW4DGU wrote:
There's one aspect of silver plating which is often not appreciated by radio amateurs, and which could result in a lot of wasted money!
The silver deposited by plating shops isn't always (or possibly usually) pure silver. The metal laid-down for decorative uses has other components which result in a surface resistivity which is significantly greater than that of polished oxygen-free high conductivity copper. Mind you, it looks good!
Most of the time polished OFHC copper is more than good enough. However, if you are planning to get an amplifier silver plated, (and it _IS_ important for cavities made from brass....) then it's important to specify high conductivity silver plating, and also to ensure that you have a few skin-depths of plating. That might mean some adjustment of physical dimensions to ensure a fit.
Rub-on surface finishes, such as Cool -Amp, can only put a very thin layer of silver on the surface. It won't be thick enough to carry the bulk of the RF current, and is more decorative than functional. It can reduce corrosion, however.
Contrary to the generally held view, oxidised silver isn't as conductive as the unoxidised metal, and it is worth using a _VERY_ thin layer of lacquer to protect the plating. The lacquer ideally needs to be based on a low-loss dielectric. Microwave oven tests of lacquered cards are a way to check this.
On 13-Nov-2002 W9IP wrote:
Chris and group -
I wonder how well polished copper covered with spray-on lacquer works. If the lacquer is high dielectric, RF shouldn't "see" it very much. Is this better than sub-optimal silver plating? It's certainly cheaper.
On 13-Nov-2002 HB9BBD wrote:
I fully agree with what Ian writes below. The Anreib-Silber comes in small bottles of approx. 1/2dl or 5% of a liter. It does not build up on itself when ribbed, however it protects the shiny surface of the brass or copper. It is hard to find even in Germany but surprisingly, everybody has it.. I got mine years back in Weinheim.
On 13-Nov-2002 JR1EDE wrote:
Oops, Silver Plating thread here too!
I bought a plating kits from Texas Platers Supply in 1999. It uses simple two No.6 dry batteries connected in series (3V) and worked perfectly in my case. I plated a few copper cans for 10GHz filters. I was told that cool-amp is not good for such application.
They don't have any web site, you must make a call or write to them. They accept credit card.
TEXAS PLATERS SUPPLY 2453 W. Five-Mile PKWY. Dallas, Texas 75233 (214) 330-7168
Another interesting source from UK: http://www.intertronics.co.uk/ Go to Products -> PCB fabrication -> HUN - Mini Plating Pens Rather expensive but professional.
On 13-Nov-2002 GW4DGU wrote:
> I wonder how well polished copper covered with spray-on lacquer works.
> If the lacquer is high dielectric, RF shouldn't "see" it very much. Is
> this better than sub-optimal silver plating? It's certainly cheaper.
It certainly is a better choice. Standard commercial silver plating has a higher resistivity than polished copper. If you choose the lacquer properly, it has no discernable effect on the Q of resonators I've measured.
I don't know what's available in N.America, but there's an Electrolube spray-on 'potting' lacquer, which I've used successfully at 2.2GHz.
A very thin 'flash' of gold plating directly onto polished copper, or high conductivity silver plating, is also worth considering.
On 13-Nov-2002 K1FO wrote:
A couple of other comments:
Silver oxide is very conductive, but often, due to our polluted atmosphere you will get silver sulfate formed which is NOT very conductive. So lacquer coating silver plating will help maintain performance over time.
Silver is only slightly more conductive than copper, so 99.99999% of the time silver plating will NOT make an RF ckt made from clean shiny copper work any better. It may keep it working better over time however.
On the other hand common brass (such as 360 free machining alloy) has about 1/3 the conductivity of copper and silver so silver plating will reduce I^R losses significantly, providing that the silver is thick enough to meet the skin debth.
It takes A LOT of silver to be thick enough to handle the skin depth. I do not have the time to find my notes, but I researched this years ago. The skin depth is not a hard and fast thickness but is defined as the debth where the RF skin currents are reduced by a certain amount, could be 20% or 30% of the maximum on the surface, but I really don't remember. Also if I remember correctly to really take advantage of silver plating on a lower conductivity metal such as brass, you need 2 mil (.002") on 144, 1 mil on 432 (.001") and .5 mil (.0005") on 1296. Common silver electro plating is on the order of .00001 to .00002". That is if you just drop off some parts at your local friendly silver plater and say "silver plate these please" without specifying exactly what you want,. you may get enough silver to only be 1/100 of what the skin depth is. You may also find that many silver plating shops will not even take your job if you want more than .0001" of silver on the parts.
Also be aware that there can be quite a bit of variation in the thickness of the silver depending on the shape of the part and even where it is in the tank when the job is done. Since there may be a -50% +100% tolerance in plating on a given part you can't just say silver plate this. You also need to specify if you want a minimum or average thickness of the plating. That is if you just say "silver plate this" generally the plater will do .00002" average thickness meaning that there may be as little as .00001" or as much as .00003" of silver on the part.
Don't be too worried about the nickel though, if it is a full service metal finishing shop they will have pure silver plating available. You can get it "dull" finish, which is pure silver as it come out of the tank and washed, or you can get "bright" finish which uses a selenium agent to brighten up the finish, but there is no nickel.
I'm not running a commercial here, but in the Lunar-Link amps there is A LOT of silver. The different parts get either .0005" or .001" (minimum thickness, not average) of pure silver depending on the frequency of the amp and if the parts are brass or copper. This is expensive. Getting the plating done in quantity (100 to 200 assorted pieces at a time) ends up costing about $ 60 per amp. in silver plating cost. This is probably less than half the cost of a small quantity job, that is having all the parts for only a single amplifier done at a time.
On 13-Nov-2002 VE1ALQ wrote:
99.8 pure silver used, 0.001 inches = 25.4 Microns, in the Industry 24Microns is considered the Highly Polish-able Silver and the normal costly applied thickness unless you ask for a lighter coating, this is calculated using current + time.
At 1296Mhz and up I ask for 12microns, which can be polished, but carefully, hi. As Steve indicated 0.001 inch is very adequate for 3 skin depth at 144Mhz. Three skin depth is considered very adequate for RF application when silver plating brass, copper, aluminium, etc, etc. Note very little difference between Silver & Copper
I developed an Excel Spread sheet for this application for various metals & frequencies, if anyone would like a copy it can be found on my Web site. Regards & Thanks, Darrell
98,8 Pure Silver
One skin depth
Freq. In Ghz 0.114
Three skin depth
Freq. In Ghz 0.114
99.9 pure Copper
One skin Depth
Freq. In Ghz .144
Three Skin Depth
Freq. In Ghz .144
On 13-Nov-2002 GM4JJJ wrote:
Further info on the silver plating solution I got from Mainline in the UK last year. Tel 0116 286 5303
"The Silver Solution"
The bottle ( 1 FL OZ) was produced by a company called Sheffield Plate Polish Company Ltd (US) of 1600 Orrington Avenue, Evanston, IL 60201 USA
I have no idea if they are still in existence because I note that the instructions were dated 1986.
No info on the chemical makeup other than contains pure silver and non toxic, but it does add "wear gloves and cover work surfaces to avoid staining. DO NOT SWALLOW"
On 13-Nov-2002 VK3AUU wrote:
Some time back in my youth, I developed a method for plating silver onto copper coils. The details are a bit hazy, but as I recall, the method was as follows.
Make up a 10 percent solution of silver nitrate. Carefully add ammonia which will produce a black precipitate and while stirring, add sufficient ammonia to just redissolve the silver hydroxide precipitate. The material to be plated is then left suspended in the solution until sufficient silver is attached. As I recall, the material to be plated is best cleaned by dipping in a weak solution of sulphuric acid. Other methods of application may work, such as brushing on the solution, as may warming the solution. I found that the silver adhered very well and quite a thick deposit could be produced. Once dried, it could be buffed with a soft cloth. Make sure that the area to be plated is scrupulously clean and free of finger marks. Rubbing with alcohol to remove grease and flux is recommended, before cleaning with acid, rinse with distilled water and dry before putting on a coat of good lacquer. Handle with gloves all the time to avoid marks from greasy fingerprints. I'm not sure how well this method works on brass, and the joints will need to be silver soldered
Take care to wear gloves and eye protection and do not work on the XYL's formica bench top as the black silver stain is impossible to remove once it dries. Don't ask me where you obtain silver nitrate, try the local drug store for a start, but you may have to go to a laboratory supply house. It is not cheap. Cloudy ammonia from the hardware shop is probably OK and battery acid is about the right strength.
If anyone tries this with success, please let me know.
On 22-Feb-2011 VE7EVE made the following comment regarding the safety of VK3AUU method:
This recipe is very similar to electroless sliver plating solution, as used for making silvered mirrors, except it does not contain a reducing agent.
I remember clearly a chemistry book I read years ago. It said in no uncertain terms that this type of solution may become very dangerous over time, especially if it is allowed to dry out. As it dries out, silver can react with various nitrogen compounds, and may
in the right conditions produce silver nitride. Silver nitride is highly explosive, and can even go off by the slightest touch.
That's why it is mandatory to make only as much solution as needed for one use, and add hydrochloric acid to the remainder, to percipitate all of the remaining silver as silver chloride.
I am quoting this all from memory, and I am not a professional chemist, but I strongly suggest to add a cautionary note to this recipe.
See http://en.wikipedia.org/wiki/Silver_nitride for more info.
On 13-Nov-2002 ON4BCB wrote:
Try our methode, take a look at:
On 14-Nov-2002 W2WD wrote:
Caswell Inc. of Newark, NY has a wide range of plating kits and supplies for small DIY jobs.as well as the large projects. I have their Silver PlugNPlate kit but have not had a chance to use it as yet.
You can check them out at: http://www.caswellplating.com
They appear to ship to Canada and Europe as well as the USA.
On 14-Nov-2002 N2UO wrote:
Thanks for all the messages on this subject. To summarize, we can say the following:
Silver Plating sources:
DO IT YOURSELF: http://www.on7lr.be/special/ag/ag.htm VK3AUU message and many others Photography fixer
EUROPEAN SOURCE: http://www.andyfunk.de/aktuelles.html
US SOURCES: TEXAS PLATERS SUPPLY 2453 W. Five-Mile PKWY. Dallas, Texas 75233 (214) 330-7168
Caswell Plating 5688 Tellier Rd Newark NY 14513 USA Phone: 315 331-5141 Fax: 315 331-5143 http://www.caswellplating.com/nsindex.htm
Cool Amp in Oregon: http://www.cool-amp.com/
It's been suggested that silver plating may not be really effective because of its thickness. Darrel has some estimates on this subject (Depths vs. frequency: www.ve1alq.com). Steve, K1FO pointed out some facts based on his experience, too. The conclusion is that rub-on silver plating may not be effective to improve conductivity at RF (certainly not better than clean shiny copper), but can help prevent corrosion, and gives a nice finish.
Thanks once again to all the fellow hams that responded to my message.
(Note: I'm not showing any E-Mail
address here in order to avoid them from being collected by SpamBots. You can
possibly find the E-Mail addresses of the above OM at QRZ.COM.)
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