Featured Correct way to make 5% solution of sodium sesquicarbonate for Bronze Disease treatment.

Discussion in 'Ancient Coins' started by Theodosius, Jan 3, 2019.

  1. Theodosius

    Theodosius Unrepentant Fine Style Freak! Supporter

    The correct way to make a 5% solution (by weight) of sodium sesquicarbonate for bronze disease treatment.

    I bought a group lot lately with a couple of nice bronzes that turned out to be infected with serious bronze disease. (I know it is not a “real” disease, but this is the name ancient collectors use for this condition). Looking up the directions for making sodium sesquicarbonate on the internet I found that many of the directions were not correct and would result in a solution that was 3x too strong. There are apparently a lot of copies of an incorrect article on how to make a 5% solution of sodium sesquicarbonate floating around, that continue to propagate through the magic of cut and paste.

    See: http://www.accla.org/actaaccla/bronzediseasetherapy.html

    I put this tutorial together to help people to make a 5% solution the correct way, that is the main thing I am trying to accomplish with this thread, not describe or debate all the ways there are to treat BD. I am no an expert when it comes to fighting bronze disease, from my research, this seems like an accepted way to treat serious infections.

    A relatively safe way to treat serious bronze disease in ancient coins is to physically remove the visible fluffy green BD using brushes, toothpicks, etc. and soak them in a 5% solution of sodium sesquicarbonate for weeks to months, changing the solution every week. It helps to soak them for 10 minutes in acetone to remove wax, varnish, etc. before starting the procedure. This allows the bases in the solution to reach the chlorine ions in the BD and react with them. I like to let the coins dry out each week and check them, repeating the picking off the visible BD if needed. More BD keeps coming in bad cases for weeks to months.

    To make the solution start with: distilled water (yes, I know some people think city water is fine but I prefer to start with water with no chlorine or other unknown compounds in it), a measuring vessel graduated in milliliters, a small cup, a gram scale ($20 on eBay or Amazon), and sodium sesquicarbonate powder (available on eBay for a $5 a pound). Sodium sesquicarbonate is considered a safe chemical and is used in cosmetics.
    Start by weighing your small, dry cup, I used a soy sauce cup from the local Thai place. Keep these and their lids because they are useful for this treatment. Notice the cup weighs 2.2 grams.
    Add sodium sesquicarbonate powder to the cup until you have added 5 grams. Notice the scale reads 7.2 grams now.
    Pour the powder into the measuring vessel.
    Add distilled water until it reaches 100 millimeters. Water weighs 1 gram per milliliter. So, you have added 95 grams of water to 5 grams of sodium sesquicarbonate powder yielding a 5% solution. Stir until the powder is all dissolved. The solution will turn clear when all the powder is dissolved.
    I like to treat coins in individual cups. The sodium solution is a conductor, allowing differences in the alloys of the coins to set up electrical currents causing unknown but usually undesired electrolysis actions on the coins. The soy sauce containers are perfect for holding most coins.

    An IMPORTANT thing to note is that you need to cover the cups to prevent the water from evaporating. If the water evaporates, the sodium is left behind, and the concentration of the solution goes up. A concentrated enough solution can remove the patina completely from bronze coins (this has happened to me ☹). I have found that even 5% is enough to affect the patina on some coins. You can top up the water in cups periodically with distilled water if you notice it evaporating.

    Change the water every week. Sometimes this treatment takes months to be successful, and sometimes if the BD is deep inside the coin then it still does not work. This works best for surface infections. Do not boil the coins in this solution unless you want the patina stripped off.

    I will report on how this goes over time. In the picture I am treating a nice Carthaginian bronze and two nice bronzes from Syracuse.

    Hope this has been useful.

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  3. Ryro

    Ryro You'll never be lovelier than you are now... Supporter

    As someone who had fought many a battle with BD...This is fantastic!
    Thanks for sharing and please post before and afters of the coins.
    Hookman, Theodosius and Justin Lee like this.
  4. Justin Lee

    Justin Lee I learn by doing Supporter

    Very useful, @Theodosius!! I've read about this process a few times over the past year, always feeling nervous and so uncertain about it with regard to the right mix and saving the existing patina. Your instructions are both detailed, straightforward, and concise. Thank you!

    (And, Ooo I see Tanits!)
    Ryro, Hookman and Theodosius like this.
  5. Clavdivs

    Clavdivs Well-Known Member

    YOU my friend are the real HERO.. THANK YOU for sharing real knowledge freely and without strings attached - helping new and older collectors .. it is very commendable! THANK YOU!

    Those who want to keep knowledge close to the vest and hold it over others need to give their heads a shake. Not particularly on this forum but this seems to be a problem in our community. I have witnessed this many times. You have helped the hobby - again - THANK YOU.
  6. Theodosius

    Theodosius Unrepentant Fine Style Freak! Supporter

    Thanks folks, just trying to share what I have learned.

    Follow the link I posted for more information.

    I did not take before pictures, unfortunately. :-(

    DBDc80, Johndakerftw, Ryro and 4 others like this.
  7. dadams

    dadams Well-Known Member

    Thanks John! Great instructive thread which I hope I'll never have to use. (Knock on wood) -d
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  8. Hookman

    Hookman Well-Known Member

    Not trying to be a smartalec, but do you know how to use the tare button on your scale?

    I noticed you were adding the weight of the cup to your ingredients.
    Just put your cup on the scale and when the scale settles, push the tare button and you will have removed the weight of the container from your measurement.
    The use of the tare feature allows you to avoid adding or subtracting weights that could possibly inject a potential for a miscalculation.
    Each time you change containers, or remove and then replace the same container, re-tare the scale.

    Again, I'm not trying to be a smartalec or be offensive. Hopefully, I'm just helping.

    Excellent post BTW, and very helpful.
  9. Theodosius

    Theodosius Unrepentant Fine Style Freak! Supporter

    @Hookman I thought about using the "zero" function of my scale to have it ignore the weight of the cup. I decided the way I described would be easier to follow and would work for people whose scales do not support zeroing.

    Alegandron, -jeffB, dadams and 2 others like this.
  10. Hookman

    Hookman Well-Known Member

    Yes, you are correct , Sir. Not every scale has a tare function, but almost all of us can add and subtract. lol. When we were going to school they actually taught us stuff.
    Thank you sir.
  11. SeptimusT

    SeptimusT Well-Known Member

    As a caveat, unless you are dealing with a very severe case, aren’t distilled water soaks and manual cleaning with a bamboo skewer better as first line treatments for bronze disease? The distilled water will at least deactivate it, but also help dissolve it when combined with manual cleaning. It’s worked in every case I’ve had, and left the patina intact. But none of my cases were aggressive.

    But maybe a small dose of sodium sesquicarbonate like this is still pretty patina safe? Still certainly something I’ll keep in mind for disaster. I have a fibula with a minor case soaking now.
    Last edited: Jan 3, 2019
  12. Aethelred

    Aethelred The Old Dead King Supporter

    A truly helpful post that I plan to print and keep for permanent reference. Thank you for sharing this @Theodosius
    Justin Lee likes this.
  13. TIF

    TIF Always learning. Supporter

    @Theodosius, can you give us the correct way to make sodium sesquicarbonate? My understanding is that you can approximate it from a mixture of baking soda (sodium bicarbonate; NaHCO₃) and washing soda (sodium carbonate; Na₂CO₃), both of which are more readily available than sodium sesquicarbonate.

    I've used the following recipe found on FAC but suspect it not quite accurate or unnecessarily strong (I don't boil the coins either).

    Screen Shot 2019-01-04 at 7.03.30 AM.png
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  14. TIF

    TIF Always learning. Supporter

    Since this is a featured thread and might be bookmarked by many people, I'm going to add other frequently cited links about bronze disease and its treatment. In re-reading these links I think the FAC NA sesquicarbonate recipe posted above is too strong; the articles contain other recipes.

    Recipe for Common Bronze Disease Treatment Found on Several Websites is Very Wrong. Merrill Gibson, Ancient Coin Club of Los Angeles

    Bronze Disease: Understanding, Curing, and Preventative Treatment
    . A fabulous presentation by Jason Sanchez and Ken Harl, Ph.D.

    Corrosion and "Bronze Disease". Collector-antiquities.com. Looks like the same information as from the FAC page about bronze disease treatment.
    R*L, PeteB, Pellinore and 3 others like this.
  15. jonathan layne

    jonathan layne Well-Known Member

    would it be safe to use tarn-x to clean them
  16. TIF

    TIF Always learning. Supporter

    Tarn-X is thiourea and sulfamic acid. It is used for cleaning silver, not bronze. I'm not sure if people use it on ancient silver coins but it is definitely not used for bronze coins nor is it appropriate for treating "bronze disease".
    Alegandron likes this.
  17. Theodosius

    Theodosius Unrepentant Fine Style Freak! Supporter

    @TIF The issue with making your own sodium sesquicarbonate from baking soda and washing soda is that the amount of water absorbed by the commercial washing soda is hard to determine. Follow the link in my first post and they explain it. I think for practical purposes you can make it as your directions from Forum list, it just may be slightly different in strength than 5%. The reference in the link also cautions against boiling as it increases the chance it will affect the patina.

    Some of the coins I decided to treat this way had BD that resisted six months of continuous treatment with Verdicare (a great product for surface BD treatment). After one week of cold soaking in sodium sesquicarbonate their patina is starting to rub off a little, but the BD seems to be reduced.

    Alegandron and TIF like this.
  18. jonathan layne

    jonathan layne Well-Known Member

  19. TIF

    TIF Always learning. Supporter

    Gawd, I didn't even notice that you already posted the ACCLA link. I skipped straight to your pictures :oops: :sorry:.
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  20. halfcent1793

    halfcent1793 Well-Known Member

    The recipe given is correct. Including the part about keeping the cups covered.

    You can't make sodium sesquicarbonate by mixing baking and washing soda, because their molecular weights are different and the latter contains a variable and unknown amount of water. You MUST buy sodium sesquicarbonate, as Theodosius recommends.

    TarnX or anything else with thiourea is VERY bad for anything copper. It corrodes the copper.
  21. -jeffB

    -jeffB Greshams LEO Supporter


    I might suggest one small addition: you mention first soaking coins in acetone to remove varnish or wax, before you do the sesquicarbonate soak (in individual plastic cups). These are both great ideas -- just don't try to do the acetone soak in one of those plastic cups! Acetone loves to eat its way through many plastics. (Ask me how I know.)

    Do the acetone soak in a glass or metal container. You don't have to worry about electrolytic effects from dissimilar metals, but I still prefer to soak one coin at a time. (Then again, I'm one of those prissy modern collectors, and I don't with many things that have spent centuries in the ground.)
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