Q: Can I use a Gold Acid Test for Titanium?

August 9, 2011

Tim asked:

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.”

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Q: What common materials can be used to etch titanium?

August 9, 2011

To niggle the semantics, it depends on what is common in ones world.

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