I have what I believe to be a piece of titanium that was found on a beach in Florida. I tested it using an acid test kit. The metal tested between 14 and 18k using a gold test kit. Should titanium test like gold, or has my acid possibly gone bad?

I’m pretty sure that the acid test bottles for gold use a variety of blends of acids, with Aqua Regia being the one that actually etches gold.

Titanium will be etched by these blends, as will platinum and a variety of other metals. I don’t know at what level each titanium alloy might test. I’d suspect that common Al6-V4 alloys would result in a lower karat rating than the commercially pure grades (#1-#4).

But the acid test will not tell you that it is titanium, as opposed to platinum or tantalum or niobium.

So I don’t recommend this as a reliable alternative to the suggestions I make in “How to tell if a piece of metal is really titanium.”

Any chemistry lab would have hydrofluoric acid, the fastest way to etch titanium. Its helper molecule sulfuric acid is available everywhere (battery acid or some drain cleaners). The combination of the two makes for a smoother etch, but you’ll have to ask a chemist, why?

I’ve found a blend of oxalic acid (HCO) and sodium bi-fluoride in a grocery store laundry section bottled as a rust remover. This etches the titanium, but can leave a carbon residue, that is easy to remove.

Supposedly, concentrated oxalic acid by itself could do the job. But I don’t see how from an entropy standpoint. Also, there is the risk of carbon monoxide fumes (oxalic acid is carbon-monoxide-acid).

ABF (ammonium-bi-fluoride) is common due to its high-volume use in the nuclear industry. I’ve used this by itself at high temperatures. It behaves like weak hydrofluoric acid; essentially buffered.

The key ingredient for etching titanium is loosely bonded fluoride ions. This means that anything that will eat titanium can kill you if it gets into your system. Some people are sensitive enough that a splash of HF on the skin can kill.

Some other suggestions and cautions are here: http://www.finishing.com/134/32.shtml

But my usual recommendation is to order Multi-Etch, a balanced blend of sodium-bi-fluoride and ammonium-sulfate, shipped dry and ready to mix:  Visit http://multietch.com

I want to do a large piece of titanium (28″ x 3″ x .5″), around how many amps would I need to push through it, or how long would it take?

I have a power supply that is 12V @ ~19A, could I use this to color my titanium if I just leave it on for a long period of time?

If I color my titanium and dont like it, can I do it again and will I get around the same results? I’m scared that I will try to color it blue and get a terrible result and be stuck with it.

Okay, three questions, but the most critical one is in the title. Titanium colors are voltage controlled. A twelve volt power supply (or battery charger) would work for electroplating or aluminum anodizing, but not for titanium. More precisely, you can get the fingerprint-prone bronzes and deep purple at or under 12 volts. But not any of the other colors.

Because the final color is voltage limited, the current is less critical, in theory.  In practice I find that to reach well saturated colors beyond about 50 volts you need a supply that can support an initial surge of at least 0.1 amps/sq.in. This can be done with lower rated supplies by charging a large capacitor in parallel with the electrodes. Your total piece is 184.5 sq.in, so 19 amps should be enough.

Burrs or sharp edges can have a negative effect on your final color.

If you don’t like your color, you can subsequently anodize to higher voltages, but not lower. The best color results appear on a clean and freshly etched surface. If you overshoot a color, or get a hazy or gray result, the only recourse is to grind, polish, or etch the color off and start over.

I have used electrolytes with a wide range of pH (acidity and alkalinity) but had not been looking for the differences. Some of my favorites are phosphoric acid (pH = 1.7), ammonium phosphate (4.2) , and tri-sodium phosphate (12). Quite different pH’s, but all slam that phosphate ion against the titanium anode and drop off an oxygen atom. Borates work fairly well, too. I’ve read that alkali sulfates can be used. But personal experience says, stay away from nitrates and chlorides.

According to some guidelines/requirements for anodizing titanium medical implants, a strong alkaline should be used. I suspect that this is to guarantee that nothing living can be in the solution.

According to one for-fee article from 1985  (Studies on anodizing of aluminium in alkaline electrolyte using alternating current) found “Electrolyte pH was found to affect the growth of anodic films considerably.” But I didn’t buy it to see how. This article is not quite to the point because it a) was about aluminum, b) they used alternating current, and c) it focused on only part of the pH spectrum.

If anyone has played with pH in anodizing titanium, please let me know if you notice any anodizing differences by pH.

I’m desperately trying to find a solution to my recently-developed metal allergy as I LOVE my earrings. Titanium seems like a great option to try, but I am wondering, what is the colored coating composed of? Is there anything in that I could be allergic to?

As I explain on pages such as A short article on the physics of Anodized Titanium Color, the color layer is pure titanium dioxide. Just oxygen bonded to the surface of the metal creating a material that has been used for artificial “Titania” diamonds.

Thus this layer actually is the hypoallergenic coating that makes titanium safe. The “silver” color has a thin layer of the oxide on it, whether I want it or not. Titanium spontaneously grabs oxygen from air or water to protect itself. When anodizing or heat coloring, the higher the voltage, the thicker the protective layer becomes. But there is no practical difference for hardness or sensitivity, as the thickest layer (green) is about 0.00000003 inches thick.

I use a simple phosphate detergent as my electrolyte, then soak the ear hooks in clear water. In the 30 years since I started doing this I have had only two customers who were too sensitive even for titanium wires. I suspect it was a non-chemical tactile or contact sensitivity; the rubbing or pressure itself was causing the reaction.

Some people claim that niobium is even better for sensitive ears than titanium. They are chemically similar, and involve the same method of coloring. It’s been discussed before here: Hypoallergenic: Titanium versus Niobium

I suggest trying both, as a spare pair of wires is cheaper than another shipping charge.  Shop my Ear Hooks.

Is it possible to color titanium in an oven (to control the temperature)? If so, what temperature does the oven have to have?

Assuming a kitchen oven, the answer is, No.

If you have a laboratory oven, a kiln, or some such, then the answer is, “Probably”.

Titanium colors by heat are controlled by temperature much like anodized color is controlled by voltage. The temperature at which you should start seeing the lowest tan/bronze is about 640°F. This is easy to reach with a direct flame, but not in a household oven.

I have not found a color/temperature scale, but would love to publish one. If anyone with a lab oven wants to play with this, please share your results.

I’m trying to get a black or dark gray finish on the face of a titanium driver head. What voltage achieves that color?

Sorry, John. Anodizing produces a particular spectrum of colors limited by the first two octaves of optical interference. I explain it here.

Black and gray are shades, not colors. One cannot make titanium black by anodizing.

So, how is black titanium made? Everyone who does it is keeping the actual process a tight secret. But my  educated guess is that it is produced by implanting nitrogen into the titanium using an industrial vacuum effusion furnace. This produces a relatively thick layer of titanium nitride in a similar chemical manner that titanium dioxide is made by anodizing. But nitrogen implanting cannot be done in an oxygen rich environment, like air or water. Air is 21% oxygen by volume, and water is 33% oxygen by atoms, or 88% by weight.

Is there any value in a programmable(manual or C/C++) power supply for anodizing?

Say Vout=20+(110*N/(255)); // N=0,1,2,3,4,…255

Giving {20,20.4, 20.8,21.2…129.6, 130}

I can also make this power limited to approximately 13W(0.10A at 130VDC)

I am not selling anything! I am just wondering if this is a worth while adventure.

As a fellow electrical and programming geek, I see the appeal of the project. But practically speaking in terms of anodizing titanium, no. The color is determined by the final voltage, and the faster you get there, the better.

Also, I use down to 8 volts on occasion. And the lower voltages are more color sensitive than the higher, so it should either be 16 bit linear, or have exponential or quadratic output, as in

vOut = (((N/64)^2 + N) *120/255) + 5 // N={0…255}

But if you were to rig an x-y table to such a supply, one could then “print” in anodized colors. However, there is a limited palette. And also one would have trouble with certain adjacent colors, and have to adjust the lateral speed to be proportional to voltage, and maybe fluid flow through the dielectric cathode, and several other engineering considerations.

As such, it becomes fun and useful. But a lot more work. Then you would be able to share it on HackADay.com or Makezine.tv or some such.

In order to make such a project marketable, one would have to write the CADD end to prevent unfulfillable designs. Artists have to have limits imposed.

James asked, “Will the TSP/90 Phosphate Free products work as well as the standard TSP brands?”

An excellent question. My first impulse is, “I doubt it.” But I am not sure. The folks at ReactiveMetals.com might have some insight (that I would share here if passed along).

TSP/90 is made with Sodium metasilicate and pentahydrate. So it is an alkali electrolyte with plenty of oxygen carriers in it. So far, so good. But as a cleanser it appears to suffer from leaving behind a film; a bad sign.

If you are concerned about the potential harm of artificial phosphates in the environment, anodizing is not a significant supply. I have been using the same 8 oz. box of actual TSP for the last dozen years. That’s equivalent to a few weeks of laundry. The same batch of electrolyte can keep on going for months, by adding distilled water (the part that is used up) and an occasional pinch of TSP crystals (to keep up the concentration from the drops removed by pulling out pieces). Occasionally, I filter out the dust and bring it to a boil to make sure it stays sterile.

If you want to be even more environmentally correct, use ammonium phosphate (lawn fertilizer) and then dispose of your old electrolyte by spraying it on your lawn. I used a box of this through the 1980′s and 1990′s.

One of these days, I’ll probably expound why the lingering phosphate meme of the 1970′s was somewhat misguided in the first place.

I make stamped jewelry and I have never worked with titanium before. Can titanium be stamped with a usual tool hardened steel stamp set? A client is wanting inspirational words stamped on a premade titanium bracelet.
Another question, would my usual method using a riveting hammer and a bench block do with titanium wire to create a rivet?

The short and qualified answer is, “Yes”.

Odds are that you are working with one of the less hard alloys or grades. Titanium behaves much like stainless steel, in that it takes more force to work it than do silver and other “normal” jewelry materials. Hit harder, maybe with a bigger hammer or mallet than you use to mark silver. I use normal steel stamps, myself  (as in this picture).

Where titanium gets its tough reputation from is that it is harder than steel under pressure. Stamps and especially cutting tools wear out faster because titanium, unlike steel, doesn’t get softer at a mere few thousand psi. Silver, gold, etc are softer to start with. I used a 20 oz. hammer to strike this stamp.

I have also used titanium wire to make rivets, using an ordinary little chasing hammer to set them. Nice, soft Grade #1 wire. Here is a List of Grades and their relative hardnesses.