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.
Tips and troubleshooting
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-Etch®ing. 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.
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.
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.