HOW TO ETCH STERLING SILVER
PART II : Water Bath & Etching Pot; and Preparing your Etching Solution
Water Bath & Etching Pot
First you need to decide what you’re going to heat (or not) your etching solution in. I use a Tommee Tippee baby bottle warmer to create a water bath. You really don’t need to warm your solution for it to work, but timings will vary depending on the environment you’re etching in so doing this creates a consistent environment to etch in.
You can pick up used bottle warmers for very little (£5 in the UK) on eBay or Amazon Marketplace; and they take up very little space. You can also use a slow cooker, or any other method of water bath you have access to. Once you know what you’re going to use, you need to find a suitable container to hold your etching solution that fits in the water bath. One that has a lid.
I use a tall, round plastic container, with a plastic screw-top lid. In the UK you can buy these for £1 in Wilkos. Glass is also good as a container, but as I need a lid that doesn’t corrode or pollute my etching solution, I’m sticking with plastic.
Once you’ve worked out what size container you’re mixing for, measure the volume you want to make up. The easiest way to do this is to fill your etching container with tap water to the level you want and measure it. I’d recommend two thirds high. Pour that out into a measuring jug and note it down for future reference. Pour away the water and get ready to mix.
NB. As the crystals you’ll be using will dissolve in the solution, there should only be a small change in total volume of water used. Don’t plan to fill to the top as it’s a real mess when it spills.
Preparing your Etching Solution
First you need Ferric Nitrate in crystal form. In the UK you can buy this very easily through eBay. Expect to pay ~£23* for a 500g tub in the UK. You can safely store what you don’t use for another time. I keep crystals safely stored for years and they’re still good. Don’t buy it in liquid form as it’s more expensive and you have no idea of the dilution strength. (* cost March 2021)
You also need distilled water. I use this all the time in the workshop so have a big container. Some people don’t bother. So yes, you can use tap water; but it will depend on the mineral content where you live as to what the impact will be on your solution. If you’re going down this route, at least boil it and let it cool. Hard water will likely make your solution a bit ‘scummy’ but it will still work.
Using the ratio above pour and weigh your water and Ferric Nitrate crystals as given in the example below.
WATER: Measure 250ml of distilled water into your container.
CRYSTALS: Wearing rubber gloves, weigh 125g of Ferric Nitrate crystals into a separate non-corrosive container. A plastic takeaway container is perfect – you’re going to label it for next time or wash and recycle it. The crystals should be damp, and should have a purple hue. Be careful with this stuff – protect your scales with clingfilm and your worksurface with newspaper or a dirty rag. As I’ve said it stains! Don’t ruin that lovely kitchen worktop or brand-new workbench…
MIX: Pour the crystals into the water. Remember crystals into water and not water into crystals. The same as mixing safety pickle.
STIR: Stir with a plastic spoon or anything non-corrosive that you’ll dedicate to this process. They will turn brown.
Once mixed I like to let the solution settle, and fully dissolve for a few hours before I use it. There is no science to this but it’s what I do – you can go straight ahead and use it as soon as it’s mixed if you’re ready to go.
You don’t have to heat your solution for it to work. It will just take longer, and I can’t advise on timings sorry. Whatever you do, note it down each time you do it, until you find the right temperature and timings for you. By finding and then following a process you can get the same results every time.
A new solution will etch far faster and more aggressively than a used solution. You can re-use your solution many times. I keep solutions going for months on end with constant use. I dispose of them when the ‘sludge’ is getting too high in the pot / the etch is taking much longer. Once you get going, you will know what I mean by this.
A solution that is too strong or too hot will etch aggressively giving you an uneven etch and striation marks.
An old solution will take longer to work, but it will still etch until all of the Ferric Nitrate is depleted.
The more ‘used’ a solution gets the more ‘sludge’ you will see at the bottom of you pot. Try not to dip your pieces into this sludge, or disturb it when you're etching. If you do disturb it, wait and let it settle as it will affect your etch.
You can top-up a solution if it’s getting low (due to evaporation) by adding distilled water. You can add more crystals too, though I would advise being confident in your solution and working practices, before adding crystals to an existing solution. You can also re-use the top part of an old solution when making a new solution.
Label the lid/top of your mixed solution, and date it (I just write it on in permanent pen). Don’t mark down the side of the pot as that will come off over time in the water bath.
When not in use, store your mixed solution in an upright position, in a dark place and away from excessive heat. It will last longer.
Seal any unused Ferric Nitrate crystals in their bag or tub, place in a box, tape it down, label it and date it. Store in a dark place.