16 May 2013

Aquamarines and Moonstones

The sun went behind clouds just when I needed to take pictures of my stock of stones for a customer planning some commissions. It doesn't show these beauties at their best. "

9 May 2013

The Perils of Photo Etching!

Today I decided to have a day off making, but as I am not very good at 'resting', I decided to fiddle with some etching that needed doing. While my silver melts away in nasty chemicals, I decided to do a little technical blog post (most unlike me), on the dastardly subject of photo etching.

Those of you that know my work, know that I like to use text on my pieces. In fact I would do so much more often if it wasn't such a pain. How can there be so many ways for it to go wrong? 

Now there are all sorts of ways to apply text to silver. You can use steel letter stamps which you hit with a hammer to strike a mark (not my thing), you can take it to someone for it to be hand engraved, as trust me I have done an engraving course and I cant see me managing to engrave decent lettering on something myself in the next 50 years! They will probably do this at great expense, here in London a hand engraved Initial is £10 - £15! They can do your engraving by machine, either a hand held one, which I have yet to see good results with, or they can do it with a machine linked to a computer.

Now, I like to add my text by etching into the silver, because I can set it all up, and supposedly control it myself, and I can do it here, at home while I get on with other work. Here is how it is done... (and how it can go wrong!)

First of all, you type your text on the computer and print it out on acetate.

Then in a dark room, you use a light box to expose the text on to some special photo sensitive film.

Use some very, very fine sandpaper on your silver, and thoroughly de-grease the metal so it is perfectly clean. Look out: If you don't do this effectively, then the film will not adhere and the process will not work.

Peel the see through backing off the film and place it on the silver. Burnish it into place, using a hair dryer as a heat source. Beware: The film gets very brittle at this point, so take care that it does not crack. If it does you have to remove the film and start again.

It should look like this. Remember: The film has a see through layer on the top too. Its really important  you remember to remove that bit too. I have forgotten before, and then wondered why the 'acid' is not etching into the metal. Doh! Next you have to put this into a solution of washing soda. This removes the film from the area you want to etch (the text), and exposes bare silver. Look out: At this stage, the film can bubble and warp, and you might have to start all over again! Rubbish!

Thoroughly dry the piece. Use tape to mask the silver so no metal is exposed. Beware: If you forget to mask the back, the acid will eat into it, and your pendant would look an awful mess. 

This taped bit, has been attached to a bit of polystyrene, so it can float upside down in the etching solution I use which is Ferric Nitrate. The way Ferric Nitrate etches is to eat the silver away and the particles fall down to the bottom of the solution. If you are using Sulphuric Acid to etch, that works by bubbles coming off the silver and rising up, traditionally a feather is used to stroke the residue away from the area being etched with sulphuric! The most ideal way to use Ferric Nitrate is with a bubble tank. It warms the solution so it works faster, and also the bubbles remove the residue so you get an even etch. I don't use a bubble tank, so intermittently, I remove my piece from the solution and run it under the tap / give it a brush with a soft toothbrush to remove bits. I can also sit my container of Ferric Nitrate in a bowl of hot water to warm it.

Take your nasty chemical, and your safety gear. In a world following best Health and Safety procedures, you would use a pinny, a full face mask in case of splashes, industrial gloves, an extractor fan, as you can see there is not a great deal of that in evidence here. Just my trusty marigolds which often get removed as the best way to check the depth of your etch, is to run your nail across the text to feel if the silver has been eaten away. 

Suspend your silver upside down in the acid, check it intermittently to remove residue, and after some time you should hopefully have a nice bit of etching. 

The time taken to etch still seems a mystery to me. At the minute it's taking about 3 hours with my current cold solution - heat and age of solution make a difference. Sometimes with warm Sulphuric you can be all etched in 20 minutes. Ferric etches slowly and cleanly, Sulphuric - quicker with more 'bite', leave it too long and it over etches and your text will have jagged edges. 

Check the depth with your finger nail, or they say with a pin, but that doesn't work for me. When it feels deep enough, clean off all the blue film, and hope that you were right about the depth, as if it is too shallow, you have to start the process all over again!

Here's what you should have now. If you look at the bottom of this piece, you can see some of the solution did manage to seep under the tape at the edge. I always allow some wastage when I'm etching something. I etch a piece first and cut it out afterwards, rather than work on small disks or pendant shapes.

And these are some of the pieces I have made with photo etched text.

Now... better get off and check the bits that I am etching now. Fingers crossed!