Friday, February 19, 2010

DIY Acid Etching on Metal for Jewelry Making - Part IV: Etching on Silver Using Ferric Nitrate




















Part I of DIY Acid Etching on Metal for Jewelry covered how to transfer designs on metal.

Part II and III covered how to prepare an acid etch bath for copper and brass.

In Part IV, the same techniques apply for etching on silver, except the acid is different.  Please review Part I - III to help understand the basic etching process.

Here’s my unscientific method for etching on silver, plus how you can avoid making the same mistakes I did.

Part IV: DIY Etching on Silver for Jewelry Using Ferric Nitrate
Ferric nitrate provides a clean etch on sterling silver and fine silver.

You can buy ferric nitrate crystals at most chemical supply stores. I buy from Adchemco Scientific in Tucson, Arizona. ($60 for 5 pounds of crystals. Smaller quantities available for less $$$).

If you order ferric nitrate from an out-of-state supplier, the cost will include shipping and HAZMAT packing costs, so try to find a local supplier to save $$$. (When I was an ASU student I bought it through my local University Chemistry Store, but 9-11 may have changed that.)
Ferric nitrate crystals look like lumps of sugar with a light hues of purple. Ferric nitrate crystals should be combined with distilled water, but I confess, I use tap water and have not had any problems.

You may have more minerals in your water supply that could make a difference, but I apologize in that I haven’t researched those variables. So, to be safe, jot down “distilled water” on your grocery list and have it handy. 

When it comes to a recipe for mixing a ferric nitrate solution, I have done a bit of research and experimenting. I found that a 50/50 mix works well. So, you don't need to buy a gram scale if you don’t have one.

By now, you may be thinking, "She probably adds a “pinch of this” and a “dollop of that” when she cooks, rather than following a strict recipe." Very true! I'm attempting to show where you can cut corners and where you must be careful.

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Note: Please do not confuse ferric nitrate with ferric chloride. Ferric chloride works well on copper and brass, but does NOT work on silver.

Ferric chloride and ferric nitrate are corrosive iron salts. Although they are potentially harmful chemicals, they are much safer to use than acid. They do not have noxious fumes and are not absorbed through the skin. They will stain skin, counter tops, and clothes, so wear gloves, protect your working surfaces, and wear old clothes when etching.

To be safe, please read the precautions listed in the Goss Studios article on etching, sent courtesy of Art Chemicals.com. I have never experienced fumes or flammability, as mentioned in the article and am not cavalier about handling chemicals, but feel that some precautions are overkill.

I smile when I see a warning on a paper coffee cup: “Caution, hot liquid may cause severe burns.” (OK, I can see the steam - I get it. :  )
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Here is the link to the formal recipe for etching on Silver, sent courtesy of ArtChemicals.com. The article is written by Goss Design Studios.

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Goss Design Studios - Ferric Nitrate Etching Recipe
400 ml of distilled water
300 grams of Ferric Nitrate

Always add crystals to water!
NEVER water to crystals.

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My Unscientific Etching Process:

Fill a quart size (glass or plastic) measuring pitcher with 2 cups of tap water. Slowly add enough ferric nitrate crystals (about 2 cups) to make a total solution of 1 quart. Mix carefully with a wooden or plastic spoon (do not use anything metal) until the crystals are dissolved. The solution will turn a dark greenish color that is fairly clear compared to the thick, opaque, greenish ferric chloride, which is used straight out of the bottle. (I feel like I should be chanting a "Spell" while stirring, as it reminds me of a Witch's brew. : )

The instruction from Goss Studios says to “kick start” the solution with “a teaspoon of old, 5:1 diluted, nitric acid solution.” I skipped that. I have worked with nitric acid and it is very dangerous stuff. I avoid it whenever possible. If you are more daring than I, please try the Goss recipe. It may increase the strength of your ferric nitrate solution. I'd love to learn about your results.

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Note on Nitric Acid Etching

An accepted way of etching silver is to use nitric acid. I tried etching silver, using 3:1 nitric acid solution, and was very disappointed in the results. The acid quickly corroded the dry toner design and red Staedtler pen resist. The edges of the design came out fuzzy. The fumes were so bad that I decided it was not something I wanted in my studio.
However, many professional jewelers swear by it as a clean etch method. They use a stronger resist, like asphaultum, which I find messy and hard to work with.

I calculated that it costs less to use nitric acid than ferric nitrate, as it lasts longer and a smaller amount is required per etch.  Nitric acid concentration gets stronger as the water evaporates, unlike ferric nitrate, which is weakened by moisture.

It is necessary to follow safe OSHA disposal requirements.  You can get more info on nitric acid etching on the internet.
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You can etch about 20 pendant-sized pieces of silver in a quart solution of ferric nitrate before it starts to slow down and finally exhaust. I calculated that (in a perfect world) 5 pounds of ferric nitrate, at $60, should produce approximately 100 etched pendants at a cost of 60 cents per piece, just to etch.

This technique is better for creating your own special unique, one-of-a-kind designs.  This may not be an economical way to create a wholesale line of jewelry. There are more economical ways of producing a jewelry design that appears to be etched, such as having a wax model cast by professionals.

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This photo shows the original 4 inch x 2 inch, 16 gauge, piece of sterling silver intended to be a bracelet.
The design has been "ironed on" and the edges filled in with red Staedtler pen resist.  The back of the silver is covered with clear plastic packing tape as a resist to the ferric nitrate.








The transfer design was made with of a sheet of IBM transparency acetate copied on my dry toner copy machine.

The copy machine transferred a thick layer of dry toner (dark black lines) on to the acetate.

The acetate was then placed (toner side down) on the squeaky clean piece of sterling silver. I put a piece of paper towel on top of the acetate.  I placed a hot iron on top of the paper towel (for about 3 minutes) this heated the acetate and melted the dry toner on to the silver.
When the hot metal cooled enough to touch, it was placed in a glass jar of water. The acetate popped off easily, leaving the dry toner design on the silver.
I used a red Steadtler pen to touch up a couple of places that didn’t transfer fully to the silver.
The outside borders of the design were filled in with red Staedtler pen as a resist to the acid.

HERE IS WHERE I BLEW IT!

A 50/50 solution of ferric nitrate takes twice as long to etch silver as ferric chloride does to etch copper and brass.

CAUTION:   Don’t be blasé about it. I learned the hard way. Below is a photo of a nice, thick piece of silver I was etching for a bracelet. I got involved in another project and lost track of time. It was in the etch bath for 6 hours and the ferric nitrate etched holes all the way through the silver in some spots. I was miffed at my neglect (and material loss), but it was a valuable lesson. I was pleased to see that the dry toner resist held up very well the whole time. The red Staedler border ink mask did break down somewhat.  I should have taped it, but I didn't think it would be etching for 6 hours!

Since then, I always carry a loud alarm timer set for 30 minutes as a reminder to check on the etch bath. (Fortunately, I was able use the middle section of the design, so it wasn’t a complete loss. And, you can always send silver (mistake) scraps to a refiner in exchange for a $$ check.)

The back of the silver sheet was covered with clear packing tape to protect it from etching. So the etching came from the front side of the piece.

The clear acetate shows how well the dry toner melted onto the metal. Only a few spots of the black dry toner are left on the clear acetate. Most of the dry toner melted on to the silver nicely.

In case you place the iron on the design too long, delicate lines may run together. So it might take a bit of experimenting to see how long it takes to melt the toner and still retain crisp design elements.

You can always start over if the toner smears or doesn’t transfer completely. Just clean off the metal with acetone (or alcohol) and begin again. No loss.

You’ll get the hang of it after a few tries.
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Summary of Etching on Silver:

THE DESIGN

a.) Draw your design directly on silver using a red Staedtler pen.

 b.) Or, use Future clear floor wax (or fingernail polish) as a resist. Scratch out a design through the resist. You can also use tape as a resist to block off areas.

c.) Or, draw a design on paper, then scan it, resize it, and save it on Photoshop using the darkest black / white contrast available.

Print out the design in highest resolution possible.

d.) Make sure any lettering or numbers in your design are “mirror” image, so they “read right” when transferred to the silver.

e.) Copy the design at a photocopy store (or use your own copier) on a machine that uses dry toner. Set the copy as dark as possible to achieve a thick layer of dry toner on a sheet of heavy magazine paper or acetate transparency.

f.) Cut out the dry toner design copy leaving a ¼ inch margin around the perimeter.

DESIGN TRANSFER TO SILVER
a.) To recap - Layer design, silver and paper towels, per diagram as shown:

(Make sure your flat workspace is not harmed by the heat of the iron. I have scorch marks on my dining room table!  An old desk or wood table works well. Must be completely FLAT. An ironing board does not work.)

b.) Heat an old iron to hottest setting. (Note: A newer, expensive iron that has an “automatic shut off” won’t work.)

c.) You can use an old electric skillet, set at 350 degrees, just reverse the order of the diagram above so the silver design is facing up. Use something very flat and very heavy (an iron?) to lay on top of the design. Don’t wiggle it when you remove it or it may smear the melted toner. It helps if the weight has a handle so it can be lifted straight up easily.

d.) The iron (or skillet) remains in contact with the silver until the dry toner melts on the metal.
Note: The time may vary depending on the thickness of the silver, depth of toner and heat of the iron (or skillet). You can hear the iron and the skillet thermostats clicking on and off to maintain the temperature.

e.) When you lift the iron off the metal, don’t remove the paper (or transparency acetate) from the silver. Let it cool down slowly.  When it is cool enough to touch, carefully pick it up by the edges and drop it into a glass jar of water. When it is cool, you can pop off the transparency acetate or soak off the magazine paper, leaving the dry toner layer that has melted onto the silver.

f.) Tape off areas of your design (such as the back) that you do not want to etch.

g.) Attach silver (dry toner side down) to a piece of Styrofoam, or a piece of plastic bubble envelope, so it will float (like a flat bottomed boat) on top of the ferric chloride etch bath.

THE FERRIC NITRATE ETCH BATH

a.) Using a plastic or glass container, wide enough to accommodate your silver “boats,” mix 50:50 solution of ferric nitrate. Container can be shallow in depth since the silver will be floating on top of the ferric nitrate solution.

Make sure your ferric nitrate container is sitting on top of, or beside something that vibrates, (Part III refers to dryer or aquarium air pump) to help move the etched particles off the metal.

b.) Set timer for 30 minutes and lay the silver “boats” on top of the ferric nitrate solution.

c.) Check every 30 minutes for level of etch you wish to achieve for your design.  (I admit that sometimes I quickly stick my fingers into the ferric nitrate to pluck out a floating boat, and all it does is stain my fingers a bit.  If washed off quickly, no stain on skin, but sometimes need to soak fingernails in weak bleach solution to remove the stains later that night.)

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Note: I found it necessary to rinse off gunk that accumulated on the design side of the silver "boats" every 30 minutes or so.  This was not necessary for etches on brass and copper using ferric chloride. 

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Also check for any missing areas in your design that may have deteriorated. You can rinse off the ferric nitrate and repair missing areas with red Staedtler pen if needed. Then return to acid bath.

d.) When design is etched to your satisfaction, remove from ferric nitrate and place in separate solution of 3 TBL baking soda and 1 cup water. When the solution stops fizzing, remove the silver and rinse thoroughly in water.  Remove all tape and rinse again. 

e.) Make sure you put a secure (plastic) lid on the ferric nitrate solution.

Admire your etched design!!!


6 comments:

Sharman Martin said...

Hi Virginia, I have some brass bullet shells that I would like to etch but the metal seems quite thin. I don't want to put a hole in them. Do you have any advice? Thanks, Sharman

Esprit Mystique said...

Sharman,

What caliber bullet shell are you trying to etch?

I have etched a wide variety of brass bullet shells, and I haven't had any problems using ferric chloride. It is a very slow etch and you should get a satisfactory etch depth in about 30 minutes with fresh ferric chloride.

Make sure you have the open end of the bullet shell plugged up so the acid is NOT able to enter the inside of the bullet shell. You can plug it with a wooden dowell, play doh, polymer clay, etc.

Make sure the dowell is floating, and not sitting on the bottom of the etch bath. Also, make sure the etch bath is moving, either from aquarium pump vibration or vibration by placing it on top of a running dryer.

After you have used your etch bath several times it may take a bit longer to reach the same depth of etch. I wouldn't worry about etching all the way through, really. Brass bullet shells etch very evenly.

It's fun to experiment. Just pull the shell out of the etch bath every 20 minutes or so, rinse it off and see how it is doing. Take notes and soon you'll have it down pat.

Go fot it!

Sharman Martin said...

Hi Virginia,
Thanks for responding so quickly. I know nothing about guns but these shells have "45 auto" on the ends. My girlfriend gave them to me as I just did some etching in a silversmithing course. I'll give it a try and check the depth of the etch often.
By the way, I bought individual red Lumocolor pens in "F" (fine) and "S" (super fine?) at art supply stores up here in Victoria, BC, Canada. I would bet that you could find them in Tucson. They allow for much more detail and control.
Thanks again for the tutorial.
Sharman

Virginia Vivier said...

Sharman,

It's great to hear that you found Staedtler pens with fine point in Victoria. I would like to hear how they hold up in Ferric Chloride or Ferric Nitrate?

I have tried other Staedtler Lumocolor pens but they broke down in the acid bath. The only pens I have had success with are "Staedtler Lumocolor CD-R Pens.”

Were the fine point pens you purchased "CD-R" or just "Lumocolor?" I believe there is a difference. But I will be very interested in hearing the results of your project. Perhaps any red Staedtler Lumocolor pen will hold up in the acid bath.

Anonymous said...

hello, thank you for such a good report on etching. Have you ever tried to etch gold? Ive heard its done with cyanide?? sound a bit suicidal to me. Do you know of any other options?
thanks
josh

Virginia Vivier said...

No, I have never tried to etch on gold. It seems a shame to remove ANY gold since it is so pricey! But I believe it can be done with nitic acid (also very nasty!). Your best resource would be to join (free) The Ganoksin Project, or visit www.Ganoksin.com. It has over 220,000 pages of resources and tutorials on anything having to do with Metalsmithing and Goldsmithing. They have articles in their archives that will explain how to etch gold and what safety precautions are necessary.

Have you tried engraving? Or, casting gold? Might be an safer way to go.

Hope this helps!