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Mechanical Memories Magazine

Issue: 2006-December - Issue 8

Ferric Chloride
By Jeremy Clapham
Very useful stuff for preparing brass for working on, decrapinating pennies and
making etched brass signs. All in all it's lovely stuff, but don't put it in your tea.
I first came across this stuff twenty years ago when I was on the fringes of a group
that collected and restored old stationary engines. They were using it to bring old brass
that had deteriorated to the point of looking blackish green back to a shiny gold lustre.
By trial and error I discovered that you need to handle it carefully and use it sparingly,
otherwise the piece you're working on shrinks before your eyes and your fingers look
like you've been smoking sixty Woodbines every day since you were born. There are
other warnings, and I list them here because I want to be responsible, but don't let me
put you off buying it, especially if you are into restoring old machines. It also goes by
the names of Chloride Hexahydrate and Ferric Trichloride Hexahydrate. The Material
Safety Data people describe it accordingly:
Health Rating: 3 - Severe (Life)
Flammability Rating: 0 - None
Reactivity Rating: 2 -Moderate
Contact Rating: 3 - Severe (Corrosive)
Storage Colour Code: White (Corrosive)
Lab Protective Equipment: GOGGLES & SHIELD; LAB COAT &
APRON; VENT HOOD; PROPER GLOVES (Proper gloves???? ..... eh)?
Having just read that this is nasty stuff and to be handled only when dressed up like a
refugee from a mad professor film, it might seem curious that anyone can buy it. When I
first bought some back in the 1980s, although nobody questioned why I wanted it, I did
have to sign the poisons book in my local branch of Timothy Whites' (remember them)?
However, in these enlightened days it's much easier. You can buy it in liquid form from
Tandy the electronics hobby store (also known as Radio Shack) or Maplin Electronics,
which have 114 stores nationwide. They sell it in little dried rocks, looking a little like (I
suspect) crack cocaine (only a guess).
So what's it used for? Well, Tandy and Maplin is a bit of a clue. The electronics
lads use it in the manufacture of printed circuit boards (PCBs ). The PCB starts off as a
sheet of fibreglass with a thin layer of copper. Using transfers, they outline the route
they want the circuit to go between the components, and then the whole thing is dunked
in Ferric Chloride. Within a short period (depending on the strength of the solution), the
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chemical dissolves the copper not protected by the transfer. After washing off and
scraping the transfer away, you're left with the PCB covered in lines of copper, which
form the circuit. So shops tend to sell it as 'Circuit Board Etching Solution'
"Marvellous" I can hear you all yawning. "So what?" Well, following the principle
that it eats away the bits you don't cover up, then a sheet of brass from the hobby shop
can be transformed into personalised keyrings; 'pennies only' signs or in fact anything
you want to etch onto a brass tag. It's important to remember that it's not just the writing
you need to protect, but also the edges, backs and any borders you would like to keep in
relief. I've realised over the years that you don't need to etch very deeply to get a good
effect, and using a solution diluted with water gives you much better control. When it
comes to applying the writing and the borders, you may like to use Letraset type
transfers. However, ensure they are well stuck before immersing, because if they float
off or peel, then the solution will attack the bit you want to keep. Alternatively, if your
hands are steady enough and your eyesight is up to it, then you paint on what you want
to preserve.
For decrapinating old pennies, mix up a weak solution in a bucket and tip in your
pennies. Stir them with a stick until you see their colour change, then rinse them in fresh
water to neutralise the solution. And voila! Sparkling coins. This will of course devalue
any valuable ones to a coin collector, but now they'll slip through your machine. Leave
a 2np in a strong solution over night and see what you're left with.
Just don't put it in your tea ........ or inhale ........ or ingest.. ....... Gulp!
Thanks for the chemistry lesson Jeremy. Before publishing this issue, 1 've invested in a
good number of Map/in shares, hoping to cash in on the sudden influx of orders for PCB
etching solution! As for decrapinating old pennies, what ever happened to 'Baker's
decrapinated pennies?' Remember them? The thought of Clive attired in Goggles &
Shield; lab Coat & Apron; Vent Hood; Proper Gloves ..... . Hmmmm, the mind boggles.
Happy New Year everyone!
•
Due to the fact that everything seems to grind to a halt at this
time of year, I'm not sure when the January issue of the
magazine will be out. I' 11 aim for the first week of the month,
but if it's later, please don't send out a lynching mob!
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