Back to Ganoksin | FAQ | Contact

Etching platinum tube

Hi, Any one have ideas on how to etch out a copper core from a platinum
tube? The tube is about 4mm dia. on one end and 2.8mm dia. on the
other. I have tried pure nitric acid cold and ferric chloride cold.
The nitric works but takes weeks. The ferric chloride works but is
still not through after weeks. I think ether would work if I agitated
them.But I don’t want to boil them, any ideas?

Duncan Miller

    Hi, Any one have ideas on how to etch out a copper core from a
platinum tube? 

I once had the experience of nitric acid not removing a copper core
quickly enough. My solution involved heating gently until the reaction
generated enough of it’s own heat to sustain the speed of the reaction.
Once this temperature was achieved it didn’t take long at all. I have a
cheap hot plate for just these kinds of days. Be sure to do it outside,
as the fumes are extremely corrosive. Bruce Holmgrain JACMBJ

Hello Duncan; Etching in a recess will be much slower because as the
solution expends it’s ability to react with the metal, it can’t get
out of the way for fresh, more reactive, solution to advance to the
site of reaction. You need something to agitate the article. Here’s
an idea: A small electric motor could be equipped with a metal rod
with a u-shaped bend in it. It would need to be a slow motor, like
one in an inexpensive electric clock. Suspend the article in the
solution with monofilament line, like fishing line, from the bottom of
the “U” in the rod. As the motor turns, the article would be raised
and lowered in the solution. Also, ferric chloride (which would be my
choice for copper), actually works better if you thin it down a bit
with water. You can heat it also (I wouldn’t want hot nitric acid),
and this will speed up the etch considerably. You could also put the
article in a beaker and suspend it in an ultrasonic cleaner, but it’s
still going to take a long time to etch out a solid core of copper.
I’m assuming you’ve cast over a copper core. Next time, perhaps you
could use a copper tube and have less to etch out.

David L. Huffman

I would try using a somewhat diluted nitric acid in your ultrasonic
cleaner. Half strength acids seem to generally be more active
dissolving metals than concentrated acids & agitation to get rid of
the dissolved waste is a priority if new activity is to proceed. Thus
a glass beaker floating inside an ultrasonic is ideal continuous

Mark Chapman

An article in AJM April 2001 p. 91 has a good idea for speeding up
the etching process, although the article is about etching silver
using ferric nitrate. It reads that the technique was already shared
on Orchid (without stating when); a search might weed it out. A cheap
aquarium pump is duct- taped to the container to vibrate and speed up
the etching process to 2-3 hours. I have not used this process, but I
remembered reading it when I saw your posting. If you don’t get the
magazine and/or can’t find the posting, contact me and I’ll fax it or
send you a photocopy if you want. Good luck, Amy

Duncan, you say you’ve tried pure nitric acid. If by that you mean
concentrated nitric, or even fuming nitric, then try adding some
water. Concentrated nitric acts as a stronger acid if it’s got a
little water there. Heating it up a bit makes a big difference,
doesn’t have to be boiling. Avoid breathing the brown fumes that come
off … no need to get paranoid, just avoid them and take sensible

If you could get a bit of inert thin plastic rod that you could push
up the tube every few minutes, whilst it’s immersed, it would displace
the partially used solution and allow fresh in when you withdraw it,
which would also speed things up.?

Kevin (NW England, UK)

Why don’t you just heat up the platinum tube and melt out the copper?
Any remnants can then be easily disolved with dilute nitric acid.


The AJM article Amy refers to originated from an Orchid post by Karen
Christians on August 20, 2000. The topic was “Open this for Ferric
Nitrate silver etching.” I think all the relevant information
contained in the post is in the AJM article.

If anyone can’t find the AJM article or the original post in the
archives and wants to see it, just drop me an e-mail and I’ll forward
it to you: I keep all this stuff on file for close to forever. :wink:


Suzanne Wade
Phone: (508) 339-7366
Fax: (520) 563-8255

   Why don't you just heat up the platinum tube and melt out the
copper? Any remnants can then be easily disolved with dilute nitric

Might not the copper amalgamate (alloy) with the platinum under these
conditions? I don’t know for sure, just wondering (suspiciously!)

Kevin (NW England, UK)

I wondered that myself, but with the large disparity in melting
points between the two metals that may not be much of a problem. I’ve
also wondered how the copper got there in the first place. Was molten
copper ever in contact with the platinum tube? If so, and some
alloying has taken place, then I suspect etching the copper out won’t
do much good. John <@johnjuan>

I pulled the platinum tube though a draw plate with a copper wire in
side it, so that I could bend up the thin wall plat. tube without it