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 Replies: 29 / Views: 2,508 |
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Valued Member
Italy
284 Posts |
Good day all!  Distilled water washes/baths are a common and widely used "first step" in conserving coins. Citing the creator of Verdicare, they are the first step of the solvent polarity ladder. I wish to drill down a bit on the technicalities of the process and hopefully some of the resident chemists of the forum will give some advices!  First of all, distilled water which we will use in our homes is exposed to atmospheric CO2, so it's slightly acidic. One could argue tha being a mild acid is a good bonus for cleaning in absence of verdigris. However, verdigris "feeds" on acid so that could be counter productive. It was advised in some discussions to add some sodium bicarbonate to slightly counteract this. Does anyone have an opinion on which % to use? As an example, using this handy website https://www.aqion.onl, we see that at 2% we should have a pH of 7.6 (room temp) or 7.3 for 1%. What concentration would be the best? It's worth noting that we are not trying to create an Alkali wash (like described in this great article: https://www.prodetecting.com/blog/c...-alkali-wash ) but simply do a distilled water wash which doesn't benefit verdigris. It should be added that if we make such a wash, a final rinse in pure water is probably needed to wash away salt deposits. The second aspect which is not often talked about is the temperature of the water. At what temperature is best to do our washes? Obviously as temp increases so does the reaction rate of the solvent (water). Too much could however ruin patina? Too cold would make the process slower or not efficient. The third aspect is how long and how many washes to do? I often read something like "wash for x hours or days" however I also read that changing water frequently will yield better results (after all, the water will get dirty as it removes dirt, loosing it's solvent-ness). By reading transcripts on museum conservation I often see 3 washes. For how long though? There is also the matter of how the coin is laid while submerged. If laid flat, it will need to be flipped. How to insert this step in the various cycles? This need could somehow be mitigated by allowing some water to be also under the coin (imagine something to raise one of the side, forming a triangle). Though I still think flipping is best. The fourth aspect is the routine in between baths. Leaving the coin outside until fully dry seems to be advised. For how long? And should heat be a tool in this step, so to force the coin to expand ever so slightly? I guess some expansion/contraction will help dislodge debris? if so how and how much? I read sun could be a tool at our disposal here but at the same time I think it might be too much powerful. Obviously no rubbing of any kind, just dry on a microfiber cloth and possibly using a rocket blower to help remove water. The fifth and final aspect is how to deal with the removal of the coin after a wash. We want to help remove what has been deposited on the coin's upper surface. Given that distilled water is harmless and plentiful, I guess a container with some of it and just swirling the coin around with our fingers could do the job (i.e. no need to use a flow like with acetone to avoid contact). In case of a salted water bath, I suppose this could be plain water. To summarise, the points which could benefit from discussion are:  Plain or "salted" water? Which concentration for "salted" water? Which temperature for the water? How many baths and for how long and what about coin flips? How and for how long to dry? Trigger thermal expansion between washes? How? How to handle removing coin from a wash (rinse)? While most will probably think things like "you are overthinking" or "this is just over the top" .. I still feel one should analyze the details and then choose if and where to cut corners. Ultimately I just wanted to write all the ideas I've been tinkering with down and I hope this triggers an interesting discussion!  Thank you if you'll wish to share your thoughts/experiences/advices! Cheers!  |
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Moderator
 United States
56855 Posts |
Just a note: distilled water comes in many levels of "distilled". I make my own distilled water for decades now and test it with every batch. I have tested store bought distilled water many times over the years and it is not a high quality most times. Also,when you say, "pure water", pure water is next to impossible to come by from what I have read. BadThad is the guy who made VerdiCare, let's wait for his input John1  |
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Moderator
Australia
16805 Posts |
Quote:
Plain or "salted" water? Plain. Especially for copper/bronze coins, you don't want to be adding any salts as this can encourage bronze disease. The pH of water exposed to normal Earth atmosphere is not significantly acidic. Rain water - especially storm water - is slightly acidic due to the slight concentration of nitric acid generated by lightning. So unless you're trying to remove actual corrosion, just plain water is what you want. Quote:
Which concentration for "salted" water? Zero; see above. Quote:
Which temperature for the water? Room temperature is fine. Adding extra heat in theory helps with solubility, but you then have the issue of "how to heat up distilled water without contaminating it". I have an ingenious method for creating "boiling distilled water" at my lab at work, but most of us (including me) don't have this gear available at home. Quote:
How many baths and for how long and what about coin flips? More than three successive baths is redundant. Flip the coin between each bath. Quote:
How and for how long to dry? Acetone is an excellent drying agent, so if you've already got some at hand (in anticipation of needing to use it on your coins), then use it. If you don't have or don't want to use acetone, drying a water-washed coin properly is important. I always pad dry with tissues (no wiping, just place the coin down on a tissue, then flip it). Allow to air dry at room temperature for at least a day before sealing it up. You could probably use a very cool oven (like, 30 deg C or so) to speed up the process but I wouldn't want to go higher than 50 deg C especially for lustrous copper as this would cause faster oxidation of the surface. Quote:
Trigger thermal expansion between washes? How? Um, no. You definitely should not be heating or cooling your coin enough to cause any significant expansion or contraction of the metal. Any possible benefit from doing this in terms of dirt removal is far outweighed by the damage caused to the coin from exposure to extremes of heat. Keep your coins at room temperature. Quote:
How to handle removing coin from a wash (rinse)? I've always found that using gloves with coins just makes things worse all round. Plus, gloves are likely to depolymerize if you end up using acetone. Wash your hands, then use your fingers. Grow your fingernails long, if you don't want your fingertips getting in the water and contaminating it. I've found having long fingernails on at least one hand really helps in the lab on occasion. Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis
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Valued Member
 Italy
284 Posts |
Quote:
distilled water comes in many levels of "distilled". I make my own distilled water Me too! As a matter of fact I just finished a fresh batch.  I use of of those electric distiller. Probably not 100% pure but seeing how much gunk is left behind.. From what I gather most cheap distilled water that is found in the store is just demineralised and not distilled? |
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Valued Member
Italy
284 Posts |
Thank you Sap for going through my madness! Much appreciated!  Quote:
Plain. Especially for copper/bronze coins, you don't want to be adding any salts as this can encourage bronze disease. The pH of water exposed to normal Earth atmosphere is not significantly acidic. Rain water - especially storm water - is slightly acidic due to the slight concentration of nitric acid generated by lightning. So unless you're trying to remove actual corrosion, just plain water is what you want. By the way, regarding the plain vs salted point, I hope I can cite something BadThad wrote on another site (google search will send you to the original content). Quote:
Verdigris and it's feed materials are acidic. The corrosion contains both organic and inorganic acids. It's good to soak for at least a few hours in distilled water with a tiny bit of baking soda dissolved in. The lightly basic wash will help to neutralize the acids because, as you can image, they play a critical role in the self-propagation of verdigris. People often use the term "bronze disease" (which I hate) to describe hydrochloric acid based-verdigris (copper chloride). Neutralization of HCl is important to older, heavier verdigris. If you want to be ultra conservative, you can just soak in distilled water with the hopes that some of the acids will solubilize. However, most distilled/deionized waters tend to be slightly acidic which is why I recommend tweaking the pH up a hair with baking soda. I'm especially worried If we plan to run washes for several days, so maybe even the slight acidity of distilled water in an open system (CO2 added) might be slightly detrimental? Obviously I'm talking about coins with verdigris. Though I almost always see some under magnification for copper/bronze coins. Thank you very much for your insights! Will reply on more points later! |
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Valued Member
Italy
284 Posts |
Took me a while but here's some more brainstorming on this topic! Quote:
Room temperature is fine. Adding extra heat in theory helps with solubility, but you then have the issue of "how to heat up distilled water without contaminating it" How about one of those mat used to slightly raise temperature (like 10 degrees?) for like plants or animals, etc? I'm not advocating this technique but it intrigues me to see what we think of it. Coins will be placed in containers above it. Quote:
More than three successive baths is redundant. Flip the coin between each bath I agree on the 3 baths but unsure when to flip. If I flip between baths then one side will get 2 while the other 1. I'm kind of more inclined to either do 4 baths (2 for each side) or 3 with a flip at half-time. By the way, what do we think the best time is for a bath? In other words: after how long the water needs to be changed to keep its effectiveness? Quote:
You could probably use a very cool oven (like, 30 deg C or so) to speed up the process [...] You definitely should not be heating or cooling your coin enough to cause any significant expansion or contraction of the metal When I was talking about thermal expansion I was thinking about something in the order of max 10-15 degrees increases. I'm not an expert, I supposed even this 10 degrees will cause a microscopic expansion which will help? No? All being said It's obviously easiest to work at room temperature! Quote:
I've always found that using gloves with coins just makes things worse all round. Plus, gloves are likely to depolymerize if you end up using acetone. Wash your hands, then use your fingers For water only I use nitrile gloves. I personally find them easy to work with if you get the appropriate size (or a smaller one). Thanks again Sap for all your contributions! Hopefully the discussion will go on! Have a great weekend everyone! |
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Moderator
Australia
16805 Posts |
Quote:
I'm especially worried If we plan to run washes for several days, so maybe even the slight acidity of distilled water in an open system (CO2 added) might be slightly detrimental? Obviously I'm talking about coins with verdigris. Though I almost always see some under magnification for copper/bronze coins. There's a difference between "soaking coins in water to remove water-soluble gunk" and "treating verdigris". If your coins have active verdigris, then a plain water soak is going to make things worse and you need something stronger. I've had some success using a neutral (pH 7.0) 5% EDTA solution. For severe "this coin is already dead" cases, Ive used ammonia. Quote:
How about one of those mat used to slightly raise temperature (like 10 degrees?) for like plants or animals, etc? I'm not advocating this technique but it intrigues me to see what we think of it. Coins will be placed in containers above it. Something like that should be fine. The other issue to be concerned with is that, at anythign above room temperature, water will evaporate much quicker so you need to seal it up. And what the seal/lid is made of can contaminate the water, if you're not careful, as your coin jar turns into a little mini-distillation device. Quote:
I agree on the 3 baths but unsure when to flip. If I flip between baths then one side will get 2 while the other 1. I'm kind of more inclined to either do 4 baths (2 for each side) or 3 with a flip at half-time.
By the way, what do we think the best time is for a bath? In other words: after how long the water needs to be changed to keep its effectiveness? The "three rinses" thing is so that each side gets a turn at being "on top", with the third and final rinse just to wash off the dirty water. As for timing, the Mk 1 eyeball is effective; if the water has changed colour or turned cloudy, time to change it out. Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis
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Valued Member
Italy
284 Posts |
Thank you very much Sap! I feel it might be beneficial to address this comment: Quote:
There's a difference between "soaking coins in water to remove water-soluble gunk" and "treating verdigris" Agreed! However as far as I understood, water baths are still the first step of verdigris removal. This does make sense to me as it is better to have a clean coin from whatever water/acetone can dissolve, before to address verdigris with products like Verdicare or EDTA or Alkali wash. So my understanding was to first carry out distilled water baths and then acetone (could also add another stronger organic solvent there) and then verdigris treatment and then closing off with what is needed (water and/or acetone -- always finishing with acetone to dry it up). My very limited experience with dirty (/in bad shape) coins tells me there's always some verdigris even if very very very little so why not always do these "salted" baths? What would be the drawback of that? (note: possible salts deposits will be taken care of the rinse in plain distilled after the bath) What do you all think?  |
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Moderator
Australia
16805 Posts |
I like to see dirty/corroded coins as "patients". And, in line with the Hippocratic Oath, my goal is "to do no harm". A corollary of this, both in medicine and in coin treatment, is to not randomly give treatments that are not necessary, since if the patient does not carry the disease which the treatment is intended for, the treatment will do no good, while the side-effects of the treatment itself can easily do harm. The chemistry of verdigris formation is complex - you won't find an accurate "chemical formula for verdigris" anywhere on the Internet, because it's a complex byproduct of numerous simultaneous chemical reactions. I don't know that this salt or that salt is harmless to coins, but I do know that salts, generally, increase the conductivity of water and thus increase the potential for weird electrochemical effects to start manifesting. So my instinctive course is to avoid it.
To continue the medical analogy, patients in a hospital go though a system of triage - treating the most critical injuries first. There's no point in stopping to take exhaustive blood tests and medical scans, if the patient is clearly and obviously bleeding from a gunshot wound - first remove the bullet and stop the bleeding, then once they are stable, consider examining the patient for other defects and illnesses.
In "coin triage", If there is obvious verdigris, then this needs to be treated, stabilized or removed first, since anything else going on with the coin is of secondary importance. Distilled water and acetone do nothing for verdigris, except perhaps remove some possible candidates for "fake verdigris", but if you've been handling bulk coins for long enough you tend to know the difference between PVC goo and actual verdigris. Bronze disease, the most aggressive form of verdigris, is so insidiously contagious, I wouldn't consider treating severely bronze-diseased coins in the same bath or bucket as unaffected coins.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis
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Moderator
United States
56855 Posts |
Joe, I sent BadThad a PM this morning. John1 |
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Pillar of the Community
Russian Federation
1555 Posts |
An interesting way to clean coins. I once had an idea, every time I replenish the collection, to dip a coin in water and soap in order to slightly clean the coin from contamination received, including during storage with another collector, but all these methods are quite time-consuming. But I like the method of cleaning with distilled water, I will try this method. How about using tweezers and pre-treating it with alcohol to remove dirt?
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Moderator
United States
56855 Posts |
I would avoid the tweezers and the soap. John1 |
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Valued Member
Italy
284 Posts |
Quote:
How about using tweezers and pre-treating it with alcohol to remove dirt? Here's my thoughts ( by no means an expert opinion). Each "solvent" (water is one of them) dissolves/addresses a specific type of "gunk"/dirt on the coin. It always make sense to start slow and add up only when needed. Alcohol is definitely stronger than water. Thus, I would only use it after a distilled water treatment. Even so, some advocate for 100% isopropanol alcohol, some for acetone, some for xylene. Reposting the polarity ladder by BadThad: http://goccf.com/t/57008#447106Other interesting posts: http://goccf.com/t/244721#2055730http://goccf.com/t/39932Edited by joe_77
03/29/2024 04:21 am
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Valued Member
Italy
284 Posts |
Quote:
[..] in coin treatment, is to not randomly give treatments that are not necessary [..] To continue the medical analogy, patients in a hospital go though a system of triage - treating the most critical injuries first [..] Sap, thanks a lot for your post and plenty of food for thought! I've actually slept on it for a couple of days so apologies for the late reply. Going with your analogy I equate the distilled water baths to "splashing some disinfectant on the patient before to do emergency care" or "want to work on a clean surface". But I completely see your point. Hopefully BadThad will help us settle the debate (the idea of adding NaHCO3; to distilled water baths comes from him anyway). As for not treating verdigris when not present, I must say (and I submit I might be misidentifying it) but on a microscopic level, I always see some on old cull/dirty coins. I keep saying to myself: let's start with some plain baths if coin has no verdigris.. then look under the microscope.. and there it is..  Like this morning I was handling this one and it looked fine with the naked eye but I see several green spots.. http://goccf.com/t/461981#4026301Of course we are in complete agreement that cross contamination is bad between coins and one should ideally always treat one at the time. I actually got a set of small petridishes with lids where you can place a coin at the time . Edited by joe_77
03/29/2024 04:59 am
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Pillar of the Community
 United States
7933 Posts |
A slightly different way of looking at Sap's excellent comments ...
1. The "polarity ladder" is mostly about dissolving stuff. Of the things I have seen mentioned, xylene or toluene (or mineral spirits) are the lowest polarity, acetone next, alcohols next, and then water. DISSOLVING STUFF DOES NOT AFFECT THE METAL THE COIN STARTED WITH. (yes, I am shouting for emphasis).
2. Once we start talking about acidity (vinegar, lemon juice, sticking the coin in a tomato), basicity (ammonia), use of EDTA, aluminum. etc., we are no longer talking about dissolving stuff, we are talking about chemical reactions, which have the potential for REMOVING THE METAL AT THE SURFACE OF THE COIN (generally in the form of reducing its salts or complexes).
Caveat lautor!
Edited by tdziemia
03/30/2024 9:07 pm
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Bedrock of the Community
United States
19930 Posts |
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It was advised in some discussions to add some sodium bicarbonate to slightly counteract this. Does anyone have an opinion on which % to use? Just a few milligrams. Going to the percent range makes the pH to high and the solution to aggressive (high ionic strength) for light, careful conservation. The goal is having the water do the work, not a buffer. Any solution made should be discarded after use. Never leave aqueous solutions sitting around - bacteria sucks. Side tip, use a clean, smaller separate container for your working water. This way you can minimize the number of times you have to open your main distilled/deionized water bottle because each exposure to air will form more carbonic acid and drop the pH. With all that said, this level of concern over water is important but not a big deal when you're using it as a conservation solvent. Water is corrosive to metal, I never recommend more than 24 hours of soaking time. If you stick to that, you'll have no problems with 99% of coin conservation projects. Don't over think it here unless you're doing very delicate stuff. As long as you're not using tap water*, you'll be fine. *I have some exceptions to this rule. |
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Replies: 29 / Views: 2,508 |
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Posted 03/18/2024 10:27 am
