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Edinburgh Etch for Silver?


#1

Hi, I really like the way that the Edinburgh Etch (4/5 ferric
chloride with 1/5 citric acid) speeds copper etching, extends the
"lifetime" of the etching solution, and reduces the amount of sludge.
Can the same thing be safely and effectively done with ferric nitrate
for silver? Or is there any other way to do something to ferric
nitrate to make it more effective or speedy? For instance, is it
helpful if the chemical is warm?

Thank you, in advance, to all those with more knowledge of chemistry
than I!

Cynthia Eid
http://www.cynthiaeid.com


#2

There are indications that the ferric nitrate etch could be improved
by adding a citric acid as a chelate former… I haven’t tried it. I
was checking on etching pewter looking at the circuit board industry
which uses proprietary strippers some using ferric nitrate some
dilute nitric acid and citric acid to remove tin solders from circuit
boards. This is a difficult etch ( called the etch from hell) that
often otherwise uses HF. Being proprietary solutions there is not
much on this and no concentrations are available. Citric acid will
chelate or tie up the removed metals in solution so they don’t form a
sludge.

jesse


#3

Cynthia, I would suggest electro-etching.

My set-up consists of a 12-volt rectifier (as used for charging car
batteries) and a series of 5 12-volt 1-watt (or thereabouts) bulbs.
These five bulbs are set in bulb holders wired in parallel to each
other, in one of the two output (i.e. dc) leads of the rectifier.

Basically, by removing / adding bulbs (by screwing them out of /
into their holders) you reduce / increase the amount of current
allowed to pass through the etching bath, and visual inspection of
the lit bulbs tells you immediately what that current is! This is
far more useful (and much cheaper) than an ammeter or similar gauge.
An in-built advantage is that you have complete protection against
accidental short-circuit, since the maximum current that can flow is
limited by the bulbs, which are of course designed for the full
voltage. One bulb in circuit means the maximum current is about 83ma
(volts x amps = watts). Five bulbs (in parallel) give a maximum
current of 5 times that, 415ma. The actual- current flowing will be
reduced from these figures by the resistance of the etching bath
itself, although one can normally arrange that that is quite low.

This method has been so simple and successful (sometimes four or
five times faster than chemical etching) that I rarely do etching
(of copper, steel, bronze, tin / pewter, silver) without it. A
related advantage is that you need minimal or no acid in the etching
bath, with the result that the resist is much less stressed. The
only time I bother adding any acid is if the conductivity of the
appropriate etching salt is not high enough in solution. In this
case I would add a drop or two of a suitable acid (nitric to ferric
nitrate, sulphuric to copper sulphate, hydrochloric or citric to
ferric chloride etc) until I am happy with the amount of current
that can flow (I’m the impatient type).

Electro-etching does not give exactly the same effect as simple
chemical etching; for one thing, metal for the most part is removed
only where there are electrical inducements to remove it, i.e.
straight-line conducting paths from the metal to the other electrode
(unless there is too much acid in the bath). I find this is a very
useful property, since chemical etching removes metal wherever there
are areas of the object to be etched exposed to the corrosive
etching solution. The etched profile is also sharper than with
chemical etching, being more vertical than U-shaped. I usually use a
bath consisting of a cylindrical plastic soup container filled with
the electrolyte and a stainless steel mesh acting as the negative
electrode, wrapped round the inside edge. The object to be etched is
suspended in the centre of the bath and connected to the positive
electrode.

I hope I have not put anybody off the process of electro-etching
since it is actually very simple and low-tech.

Paul Jelley
London


#4

Hi, Paul,

My set-up consists of a 12-volt rectifier (as used for charging
car batteries) and a series of 5 12-volt 1-watt (or thereabouts)
bulbs. These five bulbs are set in bulb holders wired in parallel
to each other, in one of the two output (i.e. dc) leads of the
rectifier.

This is quite fascinating, and totally new to me. I gather you use
this set up on both silver and copper/brass… I have a couple of
questions, though. My battery charger has one pair of leads, black
and red (negative and positive) to go to the battery to be charged.
You need both of these to make your circuit to the bulbs, right? So
where do you wire the etching bath in?

And, what do you mean, it etches in a straight line? Do you mean
that the side away from the electrode doesn’t etch, even if not
insulated?

Any chance of a photo or sketch of this set-up? I am, as I suspect
many of us are, a “visual learner”. (I never really thought much
about this until a couple weeks ago, when friends were giving me
driving directions. I asked to see the route on a map. The husband
was impatient, having just TOLD me how to get there. The wife, a
close friend of mine, got out a map for me, saying to her husband,
“Noel is a visual learner.”)

Noel


#5

Hi Paul:

I use to etch pewter, copper, bronze, sterling and hope some gold.
Are you talking about doing a “controled short circuit” in an
electrolictic solution to pass by a direct current? Do I need to use
different electrolitic solutions to different metals? Do you know
what is the composition of these electrlolitic solutions? or can you
tell me the trade marks of these solutions? can you tell me where can
I learn more about these technic? excuseme about so many questions
about it, but in the past I tried to do something like these and have
no results.

Thanks in advance.

Aurelio
Mexico


#6

There are very many procedures for etching including electrolytic on
the web and a lot in the orchid archives. some are very complete.I
have posted on this several times. You don’t need high voltage or
want it only takes a couple volts or a high current. But remember
current (amps) does the etching --voltage determines the rate. Coca
Cola straight up is a possible electrolyte for etching ( not
plating)!! Electro Etching is plating in reverse so a plating
electrolyte for the metal etched usually can be used.

A modern car battery charger may not work ( mostly the more expensive
ones) at all as they may have a system to avoid charging a dead
battery. These can blow up if charged so the safety feature has been
added.

see:

http://www.kahiko.com/Electro%20Etch%20Silver.htm

there are many more. - use the search tools.

jesse


#7

Hi Noel,

So, where do you wire the etching bath in?

I have put a picture on Orchid at
http://www.ganoksin.com/ftp/ElectroEtch1_096.gif (thank you Hanuman)
which should make it clearer.

In the picture I have marked each bulb as being provided with its
own switch; I don’t actually bother with switches, I use Edison
screw bulbs and just screw them in or out as required. The switching
current is a maximum of 83ma or thereabouts and causes no problems.
It also doesn’t actually matter whether the bulb layout is in the
positive or the negative leg of the circuit (because the bulbs don’t
have a polarity).

I have put a figure of 8w for the rectifier; 5w for the bulbs and
another 3w for a safety factor or expansion. But in practise most
commercial car battery chargers offer considerably higher wattages
anyway.

Technically yes, but only approximately, and only if the electrolyte
is ‘inert’ in the sense that it doesn’t etch when there is no
current flowing. The rate of etch at any point is proportional to
the number of ‘lines of force’ at that point. The density of the
lines of force is proportional to the current flowing and is
greatest in line-of-sight between conductors in an electrolyte, but
there are still going to be some (curved) lines of force at remoter
areas. Think of the display of magnetic field strength using a bar
magnet and iron filings, it is the same principle but using electric
field instead of magnetic field. I have found this a useful property
when etching a ring or circular bangle, by masking off the interior
with two flat circles of stainless steel mesh these short out the
lines of force from the interior. However, for maximum etching speed
I tend to add a little acid, which means I need resist even on the
’dark side’ areas, although I suffer much less from pin-holing
attacks on these areas with weak field strength.

Finally, setting the polarity and the composition of the electrolyte
bath and cathode / anode appropriately allows me to use the same
setup for electro -etching, -plating, -cleaning and -stripping,
although I would not claim to necessarily get the same quality of
results as from a dedicated bath, especially ones with features such
as temperature control, electronic current control and agitation. I
do however stand by my earlier assertion that the setup I have
described is very low-tech, simple and effective.

Paul Jelley
London


#8

Hello Aurelio,

Are you talking about doing a "controled short circuit" in an
electrolictic solution to pass by a direct current? 

I’m sorry I cannot answer this question since I don’t really
understand it. Perhaps the picture at
http://www.ganoksin.com/ftp/ElectroEtch1_096.gif uploaded by Hanuman
will answer it. I have always assumed a short circuit to be a
connection involving negligible resistance. I do indeed try and
arrange that the resistance of the etching bath itself is as low as
possible, since that removes one of the complicating factors
(resistance)from the equation, and allows me to control the current
with a separate load resistance (in the form of a parallel array of
bulbs). And controlling the current in this way removes any chance
of getting into trouble if you do cause a short circuit in the
etching bath, by for example allowing the anode and cathode to
touch, since the maximum current flow is limited by the load
resistance.

Do I need to use different electrolitic solutions to different
metals? Do you know what is the composition of these electrlolitic
solutions? 

As to the electrolytic solutions themselves, there is a huge range
of options available, from the arcane (pure water Google “colloidal
silver” if you are interested) to the draconian (strong mineral
acids with added peroxides, alkaline cyanides etc). Perhaps the most
obvious ones to use are soluble salts of the metal you want to etch,
for example copper sulphate to etch copper or copper alloys, silver
nitrate to etch silver, gold chloride to etch gold. These have the
characteristic (which can be useful) that they do not etch if there
is no current flow. Equally obvious is to use dilute mineral acids,
preferably those where the relevant salt of the metal you want to
etch is soluble (so don’t use sulphuric acid for silver!). I tend to
avoid these since they are often fairly damaging to the resist. Less
obvious are electrolytes which rely on the relative position of
metals in the electrochemical series, for example ferric salts to
etch copper and silver as with acids, etching will take place without
an applied voltage, but can be greatly speeded up with the
appropriate electro-etching setup.

You will find a huge amount of on the Internet, as a
starter you might try
http://www.ganoksin.com/borisat/nenam/gom-etching-champleve.htm (and
Jesse has recently posted a series of links).

Paul Jelley
London


#9
I have put a picture on Orchid at
http://www.ganoksin.com/ftp/ElectroEtch1_096.gif

Yes, Paul, that makes it much clearer. I still don’t entirely
understand the theory, but I hope to give it a try and see whether I
understand the practice! Thanks,

Noel


#10

Dear Paul and Jesse:

Thanks about your knowledge, by the side, googleing I found theese
address to crate an electroetcher
www.warnerknives.com/electro-etcher.htm and a anodizer
www.warnerknives.com/anodizer.htm. Are anodizing and etching the
same thing but in a diferent direciton of the current of electricy?

Sincerly
Aurelio


#11
Are anodizing and etching the same thing but in a diferent
direciton of the current of electricy?

The electrical connections for plating, stripping plating, etching or
anodizing are the Cathode (-) negative and the Anode (+) positive.
For anodizing (Usualy aluminum ) the work is connected to the Anode
or positive pole. and the cathode (-) is connected to a more inert
electrode. The same is true for plating or depositing metal the work
is connected to the anode (-). To remove material either etching or
to strip plating the work is connected to the cathode (+) . For most
electro chemical operations the voltage is very low ( 2 to 3 volts).
The current depends on the size of the object. For other than factory
work the currents are also very low.

Electro cleaning is another process used to clean parts. see:
http://www.gocctech.com/techdoc/cleaning.pdf

This uses a little higher voltage than plating or etching but still
usually will be less than 12 volts.

This is a very short operation done in a alkaline electrolyte. There
are several ways to do this - straight, reverse or cyclic… Study the
reference which is more factory oriented but it is a good guide.

Mr Warners stuff is somewhat OK but does not show the connections
clearly. His use of a variac (variable transformer) as a power supply
is not the best idea since it does not properly protect against
electrical injury. He needs to include a schematic not just a
mechanical setup.

Probably the best website for aluminum anodizing is:

http://www.focuser.com/anodize.html

If you plan on anodizing the reactive metals Titanium or Niobium
which utilize the higher voltages you had best work with Reactive
Metals Studio:

Etching and plating are pretty well described in the references
already provided.

jesse


#12
I found theese address to crate an electroetcher
www.warnerknives.com/electro-etcher.htm and a anodizer
www.warnerknives.com/anodizer.htm> 

Aurelio, the electro-etcher at
http://www.warnerknives.com/electro-etcher.htm is essentially the
same as the setup I have described and pictured, except that it uses
a transformer and full-wave rectifier instead of a battery charger,
and doesn’t have any explicit method of controlling the current. It
does however have a DPDT switch, which could allow you to reverse
the polarity in the etching bath without actually having to reverse
cables (although it is not used for that purpose on the Warner
circuit diagram).

Well, yes they use different directions of current, but they differ
in all sorts of other ways too. Etching removes metal by persuading
it to enter solution at the cathode. The oxygen that is evolved
(depending on electrolyte) at the anode has little effect on the
stainless steel usually used there. Anodising is designed to oxidise
metal such as titanium, aluminium or niobium at the anode, and
hydrogen is evolved at the cathode (again usually stainless steel).
This is not something I know a great deal about since I haven’t done
any anodising (though I probably will tinker with it when I get some
spare time).

Paul Jelley
London


#13
The electrical connections for plating, stripping plating, etching
or anodizing are the Cathode (-) negative and the Anode (+)
positive. For anodizing (Usualy aluminum ) the work is connected to
the Anode or positive pole. and the cathode (-) is connected to a
more inert electrode. The same is true for plating or depositing
metal the work is connected to the anode (-). To remove material
either etching or to strip plating the work is connected to the
cathode (+) 

Make your mind up Jesse - which is which??

Ian
Ian W. Wright
Sheffield UK