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FORVM`s Classical Numismatics Discussion Board  |  Numismatic and History Discussions  |  Roman Coins (Moderator: Severus_Alexander)  |  Topic: Is there a way to remove solder from a gold coin? 0 Members and 2 Guests are viewing this topic. « previous next »
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Author Topic: Is there a way to remove solder from a gold coin?  (Read 6534 times)
Pendrakon
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« on: December 12, 2010, 09:19:13 pm »

How hard is it to remove a glop of solder from a gold coin? Or should I just leave it like it is? Theodosius II, Tremissis, RIC 23, 14mm, 1.52 grams. I paid $150 for it which I think is an OK price including the glop. Any ideas?
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Jay GT4
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« Reply #1 on: December 12, 2010, 09:22:03 pm »

I guess you'd need to know at what temperature the solder will melt versus the temperature the gold will melt. 
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Lloyd Taylor
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« Reply #2 on: December 12, 2010, 09:34:21 pm »

How hard is it to remove a glop of solder from a gold coin?
Not hard at all, due to the low melting point of solder relative to gold.

I'd use a small electric soldering iron to heat and melt the solder (less than 450 degrees C) and remove it. You might want to determine if possible the type of solder used:
http://en.wikipedia.org/wiki/Solder

Gold melts at over 1,000 degrees C so there is not much risk to the coin if done carefully: http://www.chemicalelements.com/elements/au.html

Do you know what the solder was used for (attaching to a jewelery mount?) and what is beneath it (gouge or coin damage)? In any event, in my opinion, the coin would look better without the unsightly blob.
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Pendrakon
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« Reply #3 on: December 12, 2010, 09:54:44 pm »

OK. I have a soldering gun I use for soldering electronics. I will put a new tip on it and see if I can get the solder to melt. I definitely know it will not melt gold. When I get the solder to melt how do I remove it? Any ideas? Thanks-
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SPQR Matt
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« Reply #4 on: December 12, 2010, 10:25:11 pm »

The only thing I would like to suggest is that you first practice by applying solder to a modern penny to determine the best way to proceed with your gold coin.  Best of luck!
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Lloyd Taylor
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« Reply #5 on: December 12, 2010, 10:37:42 pm »

OK. I have a soldering gun I use for soldering electronics. I will put a new tip on it and see if I can get the solder to melt. I definitely know it will not melt gold. When I get the solder to melt how do I remove it? Any ideas? Thanks-

The solder when molten will usually bead under surface tension and can be quickly brushed away from the coin surface or wicked onto some loosely twisted very thin copper wire.

The only thing I would like to suggest is that you first practice by applying solder to a modern penny to determine the best way to proceed with your gold coin.  Best of luck!

This is probably a good idea to test the removal technique once you have a molten bead of solder on the coin surface.
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Pendrakon
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« Reply #6 on: December 13, 2010, 06:15:10 am »

Thanks- I will see what I can do this weekend.
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Lloyd Taylor
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« Reply #7 on: December 13, 2010, 01:31:16 pm »

Thanks- I will see what I can do this weekend.

Good luck. Don't forget to show us the after photo. I want to know what is beneath the blob, which seems to be very curiously placed on the coin. Although looking at it again, I think it may have served to secure a brooch pin mount at the back of the coin.
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Aarmale
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« Reply #8 on: December 13, 2010, 01:49:54 pm »

Very interesting, and good luck.  I would love to see how this coin will turn out.
How did the solder get on the coin in the first place?
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« Reply #9 on: December 13, 2010, 02:14:27 pm »

OK. I have a soldering gun I use for soldering electronics. I will put a new tip on it and see if I can get the solder to melt. I definitely know it will not melt gold. When I get the solder to melt how do I remove it? Any ideas? Thanks-

The solder when molten will usually bead under surface tension and can be quickly brushed away from the coin surface or wicked onto some loosely twisted very thin copper wire.

The only thing I would like to suggest is that you first practice by applying solder to a modern penny to determine the best way to proceed with your gold coin.  Best of luck!

This is probably a good idea to test the removal technique once you have a molten bead of solder on the coin surface.


Also if you add a little flux to the copper wire it should help to draw the solder off the coin

Good Luck
Cameron
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« Reply #10 on: December 13, 2010, 02:24:24 pm »

As a long time electronics kit builder I would recommend getting some desoldering braid (available at Radio Shack and other places where soldering irons are sold). 
Put a piece of the braid over the solder and press the soldering iron against it until the solder melts. You'll be able to tell when the braid goes flat. The braid will
soak up the solder and should remove it completely. Use an iron of no more than 40 watts. The kind of big soldering iron used by plumbers might damage the coin.
Jim A
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Pendrakon
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« Reply #11 on: December 13, 2010, 11:07:03 pm »

OK. I tried the soldering gun and copper wire removal and it looks a bit better. I will try the desoldering braid next. We will see- -. The jeweler I used said that it was an antique style hat or hair pin made from at least 18K gold. He gladly took the pin he removed in trade for his services and said the solder was old and hard. $150 is still not a bad price for a nice obverse.
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hannibal2
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« Reply #12 on: December 14, 2010, 09:58:05 am »

Just seen this.

DON'T touch it with soldering iron (or any other hot item). Gold and lead from solder form an alloy at still lower temperature. you will only make the alloy pool larger.

What i would suggest is scraping off the solder carefully (but don't dig deeper than the coin's original level). Find out first how deep any gold/lead alloy interface is.

cr
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« Reply #13 on: December 14, 2010, 10:13:55 am »

I would avoid any mechanical aproach and try vinegar. Clean vinegar is no poison and not dangerous in low concentrations. It will not harm the gold but may solve the silver content at the very surface.

First try a diluted concentration (as for salads) and ambient temperature. Some salt (sodium chloride) may help to oxidize and solve the solder metals.

If there is no effect on the solder repeat with higer temperatures and concentrations while carefully observing the gold surface.

regards
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Lloyd Taylor
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« Reply #14 on: December 14, 2010, 01:01:56 pm »

Just seen this.

DON'T touch it with soldering iron (or any other hot item). Gold and lead from solder form an alloy at still lower temperature. you will only make the alloy pool larger.

What i would suggest is scraping off the solder carefully (but don't dig deeper than the coin's original level). Find out first how deep any gold/lead alloy interface is.

cr

I think you are referring to thin film solution effects that occur at the gold/solder interface.

From http://en.wikipedia.org/wiki/Solder :
Tin-based solders readily dissolve gold, forming brittle intermetallics; for Sn-Pb alloys the critical concentration of gold to embrittle the joint is about 4%. Indium-rich solders (usually indium-lead) are more suitable for soldering thicker gold layer as the dissolution rate of gold in indium is much slower. Tin-rich solders also readily dissolve silver; for soldering silver metallization or surfaces, alloys with addition of silvers are suitable; tin-free alloys are also a choice, though their wettability is poorer. If the soldering time is long enough to form the intermetallics, the tin surface of a joint soldered to gold is very dull.

The volumes involved are very small. To my knowledge the small amount dissolved gold at the interface with the solder will not inflate the volume of the solder bubble, nor appreciably erode the coin unless you spend many hours heating and stirring the mix. So quick and rapid heating and removal avoids any problem, which is usually the case with any solder work.  In any event caution/care is warranted, but that goes without saying when it comes to cleaning any ancient coin.

Can you see any ill effects from the partial removal undertaken so far?  If so the better to stop.

The consequences of the gold in the solder at the interface are embrittlement of the join and this is a big concern in the electronics industry which regularly makes solder connections to gold.  But dissolving gold to the extent that it destroys the gold component to which the join is made is something I have never heard off.   More details on this download fact sheet: www.indium.com/_dynamo/download.php?docid=10

Certainly mechanical removal involves far greater risk to the coin.
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El Reye
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« Reply #15 on: December 14, 2010, 01:18:03 pm »

As I read this thread again, I noticed that we came to the assumption that this is a tin/lead based solder. There is a possibility that it is silver solder thus the melting point would be much higher and consequently more difficult to remove.

Cameron
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Pendrakon
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« Reply #16 on: December 14, 2010, 10:09:56 pm »

Yikes! I just put the coin in a glass of vinegar and it is bubbling and smoking! LOL! Just kidding. Thank you all for your help on this one. I think I will just leave it like it is. I only paid $150 for it and from now on I will only look at the obverse. Two years from now it will be worth more just in gold content! Thanks again for the advice-
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ras
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« Reply #17 on: December 17, 2010, 01:16:21 am »

if it were my coin i'd toss it straight into a bath of battery acid overnight. i'm not kidding. i've done it before with other high-purity gold coins (which describes most roman gold) to remove mineral encrustations.

any mechanical approach is high risk on gold (and silver too).

ras
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« Reply #18 on: December 17, 2010, 01:44:35 am »

if it were my coin i'd toss it straight into a bath of battery acid overnight. i'm not kidding. i've done it before with other high-purity gold coins (which describes most roman gold) to remove mineral encrustations.

ras

This may also work, but there is much more risk for the environment, the coin, for you and your roommate´s health.
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« Reply #19 on: December 17, 2010, 02:58:31 pm »

You want something which will dissolve lead but not gold; I'm assuming the gold is fairly pure. Diluted battery acid (always use strong acids in diluted form if possible!) will certainly do it, and if handled with reasonable care, it won't be dangerous.
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« Reply #20 on: December 17, 2010, 04:08:12 pm »

Battery acid = sulphuric acid
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Mark Z
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« Reply #21 on: December 17, 2010, 04:20:02 pm »

While I realize that this is an ancient gold coin and not an electronics project, assuming it's regular solder, here's what I would do:

Hold the coin vertically between your thumb and index finger.

Heat the solder until you can see that it is molten.

Then quickly, while still holding the coin vertically between your thumb and index finger, strike your hand down firmly and quickly so that the pad on the outside part of your hand hits the table. Don't let go of the coin! You're using inertia to remove the solder.

I can't tell you how many times I've done this to remove excess solder from a connection.

Mechanical is BAD! Don't even think of it.

OR, how about taking it to a jeweler? He/she might do it for a token fee.

mz

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Lloyd Taylor
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« Reply #22 on: December 17, 2010, 05:02:56 pm »

OR, how about taking it to a jeweler? He/she might do it for a token fee.

Good suggestion. 

I'd be very cautious of the heavy acid treatment as I/you don't know the purity of this ancient gold. A few percent impurities and the fabric of the coin could be shot by the acid treatment. Remember this is not modern gold at 99.9% purity.

Note the caveats on the acid treatment proposal:
... i've done it before with other high-purity gold coins (which describes most roman gold) to remove mineral encrustations.

... I'm assuming the gold is fairly pure.
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James A2
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« Reply #23 on: December 17, 2010, 09:35:06 pm »

Most of these comments seem to deal with damage that might have already been caused to gold by solder. A Google search for-  remove solder gold -produced pages and pages of suggestions for removing solder from gold jewelry, coins etc. I had no idea it was such a common problem. Most
suggest taking it to a jeweler, which might the best idea. Jim A

Add: MarkZ2's idea sounds interesting. I might try that the next time I have a solder bridge on a circuit
board. But I'm thinking it might not work on a glob of old hard solder that wouldn't melt all at once? I still think I would go with solder wick/braid.
If it doesn't damage a plastic circuit board, it shouldn't harm gold. It might leave some flux on the coin, but that is easily removed.
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hannibal2
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« Reply #24 on: December 19, 2010, 02:44:50 pm »

Hello,

Here are two extracts from some related material.

“” The tin in molten solder rapidly dissolves gold. If sufficient gold is dissolved, brittle intermetallic compounds can be formed in the solder joint. “”

This refers to soldering of wires to gold plated contacts (Lloyd’s comment). The problem here is not the brittle joint on soldering, which normally is very quick. It is that the gold is dissolved, especially with extended heating since both solder and coin have to be heated. And this happens at soldering temperatures.

“” Gold and lead readily form a wide range of alloy compositions. Lead has a high affinity for gold and can be used as a collector for gold in pyrometallurgical processes. The lead can be subsequently separated by volatilization.””

Alloys of gold/lead are known to occur down to 240 deg C, within the range of a decently powered soldering iron.

I still say don’t put any heat to the coin. You will only aggravate the condition.

As to mechanical scraping against chemical/acid etching, consider first some facts. You have effectively four metals in various states. The coin material which is gold alloyed (for hardening) with probably a % of copper (plus maybe silver). There is the tin/lead solder layer. There is also a gold/lead/tin alloy/s interface. Lead is quite passive in battery acid, so its left on the coin. And there is risk of damaging the rest of the clean surface by copper removal.
On the other hand solder is soft (but so is the gold) so I think a sharp blade, a steady hand and a bit of luck, will be my choice for some remedy.
I have tried the process on a silver sixpence of George IIII from a broken cufflink. It was silver solder which was removed with mixed results, for where the alloy was the discolouration persisted. The alloying elements had diffused deeply.
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