For a small fraction of the price of a bottle of copper patina solution you could be buying a lifetime’s supply of the active ingredient – and just add water.
The chemical you need is called copper(II)sulphate pentahydrate (CuSO4.5H20) and it’s a lovely colour of blue. It is less-precisely known as copper sulphate (CuSO4) which is actually an anhydrous form that works just as well. But, if you’re still using 19th Century chemistry terminology you’ll know it as blue vitriol, or cupric sulphate if slightly less out-of-date.
In the USA copper sulphate is called copper sulfate – they use the word sulfur instead of sulphur nowadays. All very odd really because a city in Louisiana called Sulphur is where sulphur was mined (see http://en.wikipedia.org/wiki/Sulphur,_Louisiana).
But I digress.
It’s the copper(II)sulphate pentahydrate form that you are most likely to encounter and it is widely available. You will find it on eBay but also keep an eye open in other places as it is sometimes available as an algicide or a root killer – just be sure to check the labelling that you’re not buying something else or some weird concoction that happens to contain some copper sulphate.
You probably already know copper sulphate. Making copper sulphate crystals is what you might remember from using a childhood chemistry set or from science experiments at school. So, keep an eye out for old chemistry sets. You’ll probably not find it in modern-day chemistry sets because it is poisonous.
Here’s how to make-up your copper patina for lead and solder…
Add some copper sulphate crystals into a plastic bottle containing water. If it looks insipidly blue, add some more crystals. Then test it on a scrap of solder or lead came. If you find it doesn’t work too well, add some more copper sulphate crystals and try again.
How hard is that?
But, it is also possible to make your home-made copper patina more effective by adding just a little sulphuric acid to make it slightly acidic. This acidification is particularly useful if you want to try depositing copper on your solder or lead work by a process known as electroplating.
Incidentally, if you’re still using 19th Century chemistry terminology you’ll know sulphuric acid as oil of vitriol.
So, how does the copper patina actually work? You surely didn’t expect me to miss an opportunity to teach you some science, did you?
You know your lead cames are made of lead. Nothing but lead, so this reaction must be happening…
copper sulphate(aq) + lead(s) → lead sulphate(aq) + copper(s)
But your solder is an alloy of both lead and tin. So, you also get this reaction on your solder work…
copper sulphate(aq) + tin(s) → tin sulphate(aq) + copper(s)
The (aq) in those reactions tells you that the named chemical is dissolved in water (Latin: aqua) and the (s) means it is in solid form.
So, you see both reactions result in solid copper and it is deposited as a thin layer, just a few atoms thick, explaining why it’s so easy to scrape off.
If you’re a newcomer to stained glass crafts I’d better tell you how to use your home-made copper patina. It’s easy, you just wipe or dab it onto your lead (or solder) and you’ll get a thin copper patina. Do it a couple of times if it looks a bit patchy.
Pure copper (as in electrical wiring) is a salmon red colour but you will notice that your copper patination tends to be a coppery brown colour instead. This is because there is only a very thin layer of copper and is oxidising quickly. To stop it getting completely oxidised into copper oxide (via brown to purple to black colours) you need to protect it from further oxidation.
The best way to protect your copper patina from oxidation is with a wax polish, for which my recommendation is any old cheap carnauba wax polish finishing compound, about which I’ve already posted a cheap recipe here.
Black patina for lead and solder’s more complicated, not because of the formulation but because of the availability of the “other” key ingredient.