Using Multi-Etch® on Your Metals

Chris Boothe

Chris Boothe, developer of Multi-Etch®

I originally perfected Multi-Etch® for titanium production. It’s a nonacid (pH 6.8) alternative to hydrofluoric acid. I’ve also tested it on other metals with great results.

Multi-Etch® can be used on the following metals:

  • Titanium
  • Niobium
  • Platinum
  • Copper
  • Magnesium
  • Aluminum
  • Zirconium
  • Nickel
  • Brass
  • Steel
  • Silver
  • Palladium
  • Tantalum
  • Mokumé
  • Meteorite
  • Bronze
  • Hafnium
  • Pewter
  • Zinc

See Etch Times and Results (PDF) for all metals tested with Multi-Etch®.

Anodized titanium unetched (top), and treated with Multi-Etch (bottom)

 

On titanium and niobium, I use Multi-Etch to remove anodizing mistakes and to clean off contamination—iron from rolling mills, heat oxides, etc. Multi-Etch will maintain the finish on titanium and niobium as long as the metal is not etched too long. Here’s a single piece of titanium that I left “as is” on the top, cleaned with Multi-Etch on the bottom, and then anodized. It looks like I anodized them separately but I did it all at once.

Copper and brass etch more quickly than titanium. You can use Multi-Etch to remove light firescale from silver but not from gold. You can clean iron contamination from platinum without removing any platinum ions. I’ve done limited testing with Multi-Etch on platinum for etch effects—that is, removal of platinum ions—and there doesn’t seem to be any effect. I have not tested it with rhodium plating but I assume there would be no effect on that either. Although Multi-Etch will etch glass, it does so too slowly to be practical for decorative etching.

I have used Multi-Etch to remove broken steel drill bits trapped in titanium and gold.

Multi-Etch will enhance the patterns in mokumé and the crystals in meteorites by etching the different metals at different rates, thus slightly raising one over another.

Here is some meteorite showing before and after treatment with Multi-Etch:

Untreated meteorite

Untreated meteorite

Meteorite treated with Multi-Etch

Meteorite treated with Multi-Etch

Although my experience is with jewelry, there are many other industries where Muti-Etch is used, such as the medical industry which uses a lot of titanium.

How to Use Multi-Etch®

How much to use and how long to etch will, of course, vary depending on what metal you use and what effect you’re after. Below are two examples.

Example 1: For a production run of two dozen pairs of titanium earrings, I use one cup of Multi-Etch in a two-cup Pyrex® container, heated to about 150° F. You can use a thermometer or look for the built in Multi-Etch bubbles which tell you when it’s ready to use (visual check.) These tiny bubbles appear when the Multi-Etch is brought up to the correct temperature. I dangle a pair of earrings from a niobium wire into the Multi-Etch for 3 to 10 seconds and then rinse in distilled water. If I did three production runs a week, I would change the Pyrex® cup about every three months. If you wait too long, the cup can shatter and make a mess.

One unit of Multi-Etch can etch approximately 1,500 square inches of titanium when dipped for three seconds at 120-150ºF.

Example 2: I manufacture a line of titanium wedding rings with platinum inlays. As all platinum fabricators are aware, the accepted method to remove cross-contamination prior to welding or soldering is a 15 minute soak in nitric acid or bisodium sulfate. With Multi-Etch®, a 15-second dip is sufficient to eliminate all impurities that could interfere with a perfect weld or solder joint. I dangle the platinum from a niobium wire into the Multi-Etch for 15 seconds and then rinse in distilled water. It’s now ready for a perfect weld.

Complete Instructions for Using Multi-Etch®

Tips and Troubleshooting

How long will Multi-Etch last?

For dry powder: at least 11 years.

For unused Multi-Etch in solution: at least 6 months (keep it capped!)

How much titanium or niobium will one gallon of Multi-Etch etch?

Approximately 1,500 square inches of titanium when dipped for three seconds at 120-150oF. As you etch, the etchant gradually becomes ineffective/neutral.

Can I restore the effectiveness of Multi-Etch after it has been used?

No, that’s why it’s best to use only as much as you need in any one sitting, leaving the rest unadulterated.

How long should I etch to remove anodizing mistakes?

If you simply went past your target color, you can dip the piece briefly in Multi-Etch and it will work backward through the colors. Be sure to rinse as soon as you see the color you want.

If the color is uneven and you want to start over, etch time will be longer than when you etched the raw metal. Just keep etching until the color disappears.

What should I use to hold the piece I am etching?

We use titanium or niobium wire bent around the piece to be anodized, or strung through a hole in the piece. You can also make a plastic holder by drilling holes in a plastic medicine bottle. Affix a handle if you want or suspend the holder from a wire made of titanium or niobium.

I’m not getting any color on my etched titanium.

If there isn’t any change in color, check your connections. After using many techniques to anodize over the last 35+ years, sometimes we still get our wires crossed!

Why is the anodized color on my titanium pieces splotchy in places?


This is the most common question. There are many variables to consider, described below.

What alloy and form of titanium are you using?

Our experience is mostly with grades 1 and 2 “commercially pure” titanium sheet and wire. Sometimes the ends of a batch of wire or sheet have a heat oxide that is very hard to remove. You also can’t see it! But if you suspect that might be the problem because most of the pieces in a batch anodize fine, try etching the “bad” pieces longer and avoid using the high-voltage colors if possible. The aircraft grade — 6/4 — usually colors well without any etching at all.

Cast titanium parts like medical implants sometimes have a whitish alpha-case from heat which must be mechanically removed (e.g., sand-blasting) If this is not removed, it may be difficult or impossible to anodize evenly with higher voltage colors. Try etching longer before anodizing.

Make sure you have degreased the metal before etching.

If the metal is really dirty, e.g., after tumbling, etch once, rinse well, and etch again. Hold the pieces by the edges so that you don’t leave fingerprints.

Did you accidentally contaminate your etching bath?!

If you introduce brass, copper or iron into the etching bath, those materials will tend to plate onto the titanium and interfere with anodizing. If that happens, you will need to throw out your contaminated etching bath and start with a fresh one. These contaminants could come from the tooling you use to form your piece–files, saws, etc. If possible, keep a separate set of tools or clean the piece with an ultrasonic before etching.

Grow the oxide slowly.

If you’re aiming for the color at 70 volts, start at 60 and, while leaving the piece in your anodizing bath, keep the voltage at 60 and see if the color continues to advance to the higher voltage color. If it doesn’t, try increasing the voltage slowly.

Make sure you rinse well after etching the metal.

If you drag Multi-Etch into your anodizing bath, it can inhibit good color. If you are not going to anodize immediately after etching, protect the clean surface by applying a 10-volt color. If you don’t want to anodize at all, then store the etched pieces in distilled water. This will allow you to wait months if necessary, before anodizing.

What are you holding the titanium with while anodizing?

Using something other than titanium or niobium as hanging/holding wires when anodizing can prevent the voltage getting to the titanium. Some metals, such as copper, brass, gold, etc. will draw off the voltage. Some people use a plastic container with a titanium or niobium probe to anodize–this works great for anodizing lots of little pieces.

What is your anodizing solution?

We use 1 tablespoon of ammonium sulfate per gallon of distilled water. You can get ammonium sulfate wherever gardening supplies are sold.

Reactive Metals Studio recommends using TSP. Start with 1/8 cup per gallon of distilled water. If the anodizing reaction is too slow, add a little more TSP. For a bath of either ammonium sulfate or TSP, you can squirt a little dish detergent or Simple Green to act as a surfactant, which is important when you are after a smooth gradation from one color to another. Without that, sometimes the liquid “beads up” when lifting the titanium out of the bath.

It’s possible that if you purchased distilled water in a plastic jug that has been sitting around the store awhile, the water may have absorbed something from the plastic jug itself. Try using water from one of those purified water vending machines.

DO NOT ANODIZE WITH Multi-Etch, sulfuric acid, or detergents with fancy spot retardants.

When mixing Multi-Etch, double strength for cold etching, allow at least 24 hours to completely dissolve the Multi-Etch powder. Shaking the container before use can also help.

Sometimes everything is “correct” but you still can’t get even color in the higher voltages. This is not because of the etchant but is due to inconsistencies on the metal itself. High-voltage colors are the hardest colors to achieve so if you have a choice, choose a lower voltage color, especially for the problem pieces.

If you discover something not covered here, please let us know! info@multietch.com

Safety of Multi-Etch®

Just how safe is Multi-Etch compared to hydrofluoric or nitric acid? Well, while I would never recommend this, I have reached my hand into 100°+ F heated Multi-Etch to retrieve a part and I suffered no ill effects (all ten digits and skin intact).

Download the Multi-Etch Material Safety Data Sheet (PDF). For 24-hour emergency assistance, call 800-535-5053 (24-hour).

History of Multi-Etch®

Why did I pursue an alternative to hydrofluoric acid?

In these modern times, dying for your art is just plain stupid. Although in my youth I had my share of unfortunate experience—exploding kick presses, dense orange clouds of acid gas, and even getting shot in a hold-up of my jewelry store—as an artisan-jeweler-metalsmith with close to forty years of experience, my goal is not to die in an industrial accident, but rather, of old age.

Artists courting the muse with hydrofluoric acid need to realize the dire peril involved. Do you really want to find out years from now that your fume hood had back draft, releasing acid fumes into your studio?

I etched titanium for ten years with hydrofluoric acid but I used a full face mask with a separate air supply and a powerful fume hood. Additionally, I took air quality samples with a Draeger tube. These are gas analyzers which read in parts per billion. Yet, even with all these safety precautions, the risk was still too high.  Here is one report on the seriousness of exposure to hydrofluoric acid (PDF).  I then spent several years testing different formulations until I perfected a product that met my exacting quality standards and that I’m proud to use in my own work.

Ordering Multi-Etch®

Multi-Etch is available in the U.S.A. through:

1. Reactive Metals Studio, Clarkdale, AZ
info@reactivemetals.com
(800) 876-3434 or (928) 634-3434
www.reactivemetals.com

2. Rio Grande, Albuquerque, NM
Order online
(800) 545-6566
www.riogrande.com

Now available in Canada through The Ring Lord.

Order online (Canada only)
customerservice@theringlord.com
(855) 746-4567
www.theringlord.com

Other Uses of Multi-Etch®

I am always eager to learn more about what Multi-Etch® can and cannot do. Please email me with comments, complaints, or kudos: info@multietch.com.

—Chris Boothe, developer, Multi-Etch®