Multi-Etch® is a low-acid (pH 6.8) alternative to hydrofluoric acid and can be used on the following metals:
Click here for chart of Etch Times and Effects (PDF) for all metals tested with Multi-Etch®.
More information on select metals is below. For metals not included here, ask us or send a sample and we’ll test it for you.
On titanium and niobium, I use Multi-Etch to remove anodizing mistakes and to clean off contamination—iron from rolling mills, minor heat oxides, etc. Multi-Etch will maintain the finish/texture on titanium and niobium as long as the metal is not etched too long. Above is 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:
Although my experience is with jewelry, there are many other industries where Muti-Etch is used, such as the dental and medical industries which use a lot of titanium.
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 50 titanium parts, approximately one square inch each, 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.
How can I get the best color on titanium?
First, don’t forget to read the complete instructions! (PDF) Then read the basic steps below as well as the details that follow. Chances are you will not have any issues if you follow the instructions. But, in case you do, check out the tips below.
- The titanium needs to be degreased (Simple Green in an ultrasonic works splendidly)
- Rinse in deionized water
- Don’t heat the etching bath more than necessary
- Use holders that won’t contaminate the bath, e.g., plastic, niobium, titanium
- Right into the anodizing tank
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!
Inconsistent or splotchy color
Cloudy colors indicate the Multi-Etch bath is getting used up. One way that happens too quickly is to keep the solution heated. We recommend pouring out an amount that you can use up all at one time rather than making a bigger bath that is kept constantly heated. Second best is to heat to temp, use it and then let it cool down until the next etching session. It is particularly wasteful to keep the solution heated over a weekend and that will definitely shorten the useful life.
The holding wires which are used to suspend the titanium in the etch bath can contaminate the etching bath if they are made of steel or copper. These foreign metal ions then re-plate onto the titanium.
Another possible cause is too short of an etch time. We’ve found that seven seconds in heated Multi-Etch is ideal but some users say ten seconds is better.
Something you might try, if applicable, would be to wire-brush your titanium prior to Multi-Etching. The bright finish will be maintained if etch times are below ten seconds. This could also be used to reclaim prior-etched items that were not up to standards. When using this method, it’s very important to make sure all contaminants from the wire-brushing are cleaned off before etching.
Details on getting the best color
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. You can also put a little Multi-Etch in your tumbler.
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. Etch times for cold etching are three to seven minutes.
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, bring the voltage up to 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. 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 container, such as a medicine bottle. Affix a handle if you want (plastic would work great) or suspend the holder from a wire made of titanium or niobium, and anodize with a titanium or niobium probe.
You can also purchase baskets for mass anodizing from Reactive Metals Studio.
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. The anodizing solution does not get used up; you can re-use it indefinitely by adding more distilled water as it evaporates.
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 a purified water vending machine.
DO NOT ANODIZE WITH Multi-Etch, sulfuric acid, or detergents with fancy spot retardants.
Sometimes everything is “correct”…
…but you still can’t get even, consistent color in the higher voltages. This is not because of the etchant but is due to inconsistencies of 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.
Other questions and answers
How long will Multi-Etch last?
For dry powder: at least 11 years.
The shelf life for mixed UNUSED Multi-Etch solution is at least 8 months. (Keep it capped!)
One way you can maximize the usefulness of a Multi-Etch bath is to etch as many parts as possible before anodizing. After the titanium pieces are etched, place them into a holding tank of deionized water or base coat them with 10 volts. Either method seals the surface, inhibiting any oxidation. Later, the pieces can be anodized at the required level. We’ve tested samples that were base-coated (anodized 10 volts) and years later they will anodize vividly with the application of higher voltages.
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 120–150°F. As you etch, the etchant gradually becomes ineffective and trends toward a lower pH.
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.
If you discover something not covered here, please let us know! firstname.lastname@example.org
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). You would suffer significant damage if you tried that with hydrofluoric or nitric acids.
Download the Multi-Etch Material Safety Data Sheet (PDF) (Dry Powder).
For 24-hour emergency assistance, call 800-535-5053.
Why did I pursue an alternative to hydrofluoric acid?
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 a full-time artisan-jeweler-metalsmith since 1971, my goal is not to die in an industrial accident, but rather, of old age. I’m getting closer every day.
Artists and metalsmiths working with hydrofluoric acid need to realize the dire peril involved. I etched titanium for ten years with hydrofluoric acid and used a full face mask with a separate air supply and a powerful fume hood. But I decided I didn’t want to find out years from now that my fume hood had back draft, releasing acid fumes into my studio.
Here is one report on the seriousness of exposure to hydrofluoric acid. I 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.
When you’re ready to scale up your operation to a custom production anodizing system, contact AnodizeTitanium.com and click on “request a quote” or “hire an expert.”
I am always eager to learn more about what Multi-Etch® can and cannot do. Please email me with comments, complaints, or kudos: email@example.com.
—Chris Boothe, developer, Multi-Etch®