Dr. A.K. Williams, Ph.D

San Pedro, Costa Rica

Introduction

      When I got out of the Navy, after being around aircraft at high-power turn-up, for 4 yrs, my hearing acuity was about 20- 14,000 cps. Now, I suspect it’s about 500- 10,000 cps.

    Well guys, how the hell did we get to this point? We started out to just explain some facts about mercury. It’s your fault. Well, maybe just a little bit mine. Fact is, now that I have created a whole new group of basement chemists out there (I take credit for that). But, you keep sending requests for more and more info so it sort of means that a lot of you are hooked on basement chemistry and might never be the same again.

      Let’s get on with it. First, what do we mean by the word "assay"? It means determination of what is present in whatever sample you are working on. Doesn’t have to be gold. We can assay for silver, rhodium, sulfur, water, bubble gum, anything. Now you must understand that there are two basic classes of assays. Qualitative and quantitative.

      Qualitative tells you what. If someone brings in a sample of quartz rock and says, "I want to know what is in it". We take it to the basement and run it through our procedure and issue a report that says "sir, you have quartz, sulfides, arsenic, silver, copper, and gold". This is a qualitative assay.

      Of course, our client who is a prospector immediately asks "how much gold"? Our reply has to be "who knows". $63.00, Will that be cash or credit card? "But I have to know how much gold is in it. Great, now we can run a quantitative assay for only $89.99. Gold only. Quantitative tells you how much.

      Now I’m not telling you that everyone should run out and start buying equipment to install an assay lab in the basement. I just thought that you might like to know what is involved when you take a sample to an assay lab and why it costs what it does.

      I’m going to put in also some Q&D methods that you can do in the field to help you determine what spots have more fine gold than others do. You are going to hate me because I’m not going to tell you where this gold mine of information is located on the page. Hence, you will have to read the whole thing in order to obtain this very necessary information. You wouldn’t want to miss it, would you? That might allow your partner to know more than you. Wouldn’t want that. Naaah, you are a basement chemist and are hooked on information.

      This page is going to be very difficult to write and it’s going to take time but you guys seem to be worth it, so--- if you will hang with me we are going for a MAGIC CARPET RIDE!!

Types of Assays

Aqua Regia

      Then, hydrochloric acid is added and the evaporation repeated. This Hydrochloric reduction is repeated 3 times to be sure that all of the nitric is gone. Now you have the values in a solution of concentrated hydrochloric acid. Now add about two volumes of water. If there was silver in the ore it will precipitate as a white cloud of silver chloride. The silver is removed.

      ;At this point there are several options as to how the next step is accomplished, but the usual is to extract the gold chloride into an organic solvent, make it up to an exact volume and put it into an instrument called an atomic absorption spectrometer that measures the gold content.

Fire Assay

      The lead is separated from the glass by simply smashing it with a hammer. The lead is further pounded into a cube. This cube is weighed. The lead cube containing the values is now put into a sort of a cup with a very thick bottom, made from bone ash or cement. This cup is called a cupel. That is Q-ple not cup-l. If you drop this info at a cocktail party you wouldn’t want to mis-pronounce it.
      The cupel with the lead is placed back into the furnace and heated at 1000 degrees or so. The door to the furnace is usually left open a crack so that air can enter. At this temperature the lead rapidly combines with the oxygen in the air and is converted back into lead oxide. You see, another redox reaction. First it was reduced from lead oxide to metallic lead and now it is being oxidized back to lead oxide. I’ll explain this better when we get to luxes.

      The molten lead oxide now soaks into the cupel. Don’t ask why, it’s just the nature of the beast. Bone ash or cement will absorb large quantities of lead oxide. When all of the lead oxide has soaked in you will be left with a very small sphere of metal. This sphere contains all of the precious metals except for Osmium. In the trade they say, "if you can cupel it, you can sell it". Anything that remains after cupeling is precious metal.

      Now this tiny lump is weighed. Next it is flattened by smashing it with a hammer. This is to increase the surface area. Remember about surface area? The flat metal piece is put into a small porcelain dish and treated with 50% nitric acid until there is no more reaction. The remaining piece of metal is dried and weighed.

      The reason for weighing before and after the nitric acid treatment is that you probably want to know how much silver you had in the sample. Since the nitric acid removes the silver the difference between the first weighing and the second is the amount of silver that was in the sample. The metals remaining after this acid treatment are gold and the platinum metals.

How they do that

Assay Fluxes

      The amounts used are not correct for all ores. If your prill is too small, add more flour. I happen to know that 1 gr of flour will produce about 12 gr of lead from the litharge. So, if your prill is 10 gr too light you should add another gram of flour to the next assay. It’ll be close enough. Another thing that can go wrong is that sometimes the ore produces a melt that is too thick and viscous to pour properly. Could probably add more sand or, more effective, would be to add a couple of grams of Borax. Borax produces a thinner, more liquid melt. If borax is used you should be aware that it attacks the clay crucible so don’t use so much that you get a hole in it.
      I should also mention that molten Litharge will dissolve the crucible and the firebricks that line the furnace. That is another reason for the quartz sand in the flux. It protects the crucible.
      So, in reality, the business of Fire Assay is some science, some art, some patience and a little luck.
      I never intended to make assay chemists of you. This page is intended to, hopefully, give you a little insight as to what goes on in those mysterious backrooms that you never get to see at the assay laboratory.

Smelting

A field assay that you can do

Determination of Free Cyanide in Solution

Dr. A.K. Williams, Ph.D
San Pedro, Costa Rica
      O.K. guys, we are going on a little excursion into the world of titration. What is "titration"? Well, it’s a method of finding out something that you want to know by setting up an experiment in graded steps so that we can know when a certain event takes place. For example, If you are near deaf, like me, and go for a hearing test one the things that they test for is the frequency range that your ears respond to. A person with normal hearing can detect frequencies of about 20 to 20,000 cycles/ sec. As we get older we usually start to lose our high frequency acuity. When I got out of the Navy, after being around aircraft at high-power turn-up, for 4 yrs, my hearing acuity was about 20- 14,000 cps. Now, I suspect it’s about 500-10,000 cps.
      Anyway, the examiner will turn on an instrument that produces sound of a certain frequency and ask if you can hear it. If not, he increases the frequency and asks again. When he reaches a point where you can hear the sound, he has reached an "end point". He has "titrated" your hearing response.
      Now, we are going to do the same thing to determine how much free cyanide is present in any solution of nterest to us. I know someone is going to ask, "free cyanide, is that different from any other kind"? Well yeah, it is. "Free cyanide" is the cyanide in the solution that is not tied up by any metal or other chemical. It is "free" to react with gold or silver. Maybe "free cyanide" could mean the cyanide that the government/do-gooder complex hasn’t anaged to track down and throw in jail yet.
      Silver does react with cyanide to produce a water-soluble complex. However, if there is no "free cyanide" in solution the complex changes from potassium silver cyanide, KAgCN, to silver cyanide, Ag (CN) 2. The former is soluble (will dissolve) in water, the latter will not. This fact gives us the means to skin this cat too.
      We are going on a chemo-trip that will allow you to determine how much cyanide is in any solution that you might run into. If you think you neighbor is dumping cyanide in the storm gutter in front of you house, you can catch him! For this titration you will need a few items from your scientific supply source. You will need a "burette" of either 25 or 50 cc capacity. This should be graduated in 0.1cc increments. This item is simply a long glass or clear plastic tube, accurately graduated, with a stopcock at the bottom so that you can control the flow of liquid from the tube. You will need an Erlenmeyer flask of 250-500 cc capacity. Yeah, you could use some other clear container but everyone really ought to have a couple of these anyway. You really should have 100 or 250 ml graduated cylinder. These are things you should have in the basement anyway. You will find them useful for many purposes. You will need some Silver Nitrate in crystal form. You could make it, but better to buy a little from scientific supply or from local drugstore.
      Now, probably the most difficult part, you must weigh out exactly 13.07 grams of Silver Nitrate. This is the critical step because any error you make here will be magnified in your final results. This is your "standard Silver Nitrate solution" that you will be using for a long time. Now you put this in a container and add distilled or de-ionized water to exactly 1 liter or 1000 cc. Put this solution in a tightly stoppered bottle. A dark bottle is best but you can darken the bottle by wrapping it with black electrician’s tape. Don’t forget the bottom. You are doing this because silver nitrate is a little unstable in the presence of light.
      Now, we are going to titrate some cyanide solution. I guess you have a cement mixer running with some good concentrates in it and we have to be sure that the cyanide concentration stays about where we want it. Take out a sample and filter it through a coffee filter. Take exactly 100cc of this filtrate and put it in the flask that you bought, or you favorite hi-ball glass if you insist. Fill the burette to above the "zero" mark with the Silver Nitrate solution. Now, carefully turn the stopcock and let the Silver solution run out until the liquid is at the zero level. Now we are ready to get it done.
      There is a little art to titrating. You should be able to swish the CN solution in the flask in a circular motion while allowing the Silver Nitrate to slowly drip into it. Sort of like rubbing your stomach and patting your head at the same time. If it seems awkward, not to worry, you ain’t a pro yet. It will work; it’s just that a pro will do it a whole lot faster than you. Now to the guts of the thing. Just like the hearing examiner, you are looking for something to happen, the "end point". In this case the end-point will be when you see a permanent white precipitate (cloud) form. You will probably see a white precipitate form and in a second or two, disappear. This is not what you are looking for but it is an indication that you are getting close, so go careful. You will find a point at which 1 drop of Silver solution will make a cloud that does not dissolve. STOP! This is the end-point that you are looking for.
      Now, you simply read off the burette how many ml (cc) of silver solution that it took to get to the end-point. Due to some manipulation that I did for you that you didn’t even know about, the ml of silver solution that you used divided by ten will equal the percent of free cyanide in your cement mixer solution. If it is getting low, add a little more cyanide, etc.
      I know that you were thinking about things like "why did this character tell us to weigh out a screwball amount of Silver Nitrate like 13.07 gr.". Well, due to the magic of another science, mathematics, I was able to convert the numbers from molar values into something that would be easier for you to handle. Don’t you admire me for that? Sure you do! Mathematics ain’t Basement Chemistry, but it’s sort of handy to have around sometimes.
      Just so you will understand what went on in this titration, I’m going to explain it (I hope) in chemical terms. After all, If someone should stop you on the street and ask "sir, could you explain to me how to titrate cyanide with Silver Nitrate", You would, of course be able to tell him more than he ever wanted to know about the subject. That, by the way, is the secret to being an expert authority on any subject. When someone even mentions a ubject, you jump in and tell him or her so much that they run off screaming into the night. Now you are the expert!
      If we have a reaction going we would expect to have some gold and silver reacted with cyanide. Might be some other metals reacted also. This is not what we are concerned with. This is cyanide but it has already captured something. We are more concerned with whether or not we have enough cyanide left to get the rest of the precious metals dissolved. Free cyanide! When we titrate the solution, we are adding Silver Nitrate. We know that Silver reacts with cyanide to produce a water- soluble salt like potassium silver cyanide, KagCN. As we titrate the unknown solution with silver we are producing this compound. When the Cyanide is all used up we start to make Silver Cyanide, AgCN. This chemical is not soluble in water and will precipitate as a white cloud. This is our end-point and it indicates the point at which there is no more free cyanide in the solution. The amount of silver needed to reach this end-point tells us exactly how much cyanide was in the solution. Does that make sense to anyone? If not, let me know and I’ll try to explain it some other way
      At this point I can just see a whole bunch of you, who would otherwise be watching TV with a beer or two, down in the Basement oxidizing, reducing, titrating, and extracting all sorts of great things. DAMN, I LOVE IT!!!

by James A. McCulloch

      As all detectorists are aware, long-term burial in corrosive soil, or immersion in salt water, doesn't do the appearance of most metallic objects any favors. Regrettably, tarnish, rust, and corrosion are the natural consequences of chemical interaction with most metals.
      Many methods have been devised to remove the various forms of oxides, sulfides, carbonates, chlorides and assorted types of verdigris from metallic objects. The method employed most often by professional conservators of recovered metallic objects is electrolysis, a process wherein the object to be cleaned is submerged in a special, electrically-charged chemical solution which causes to corrosion to disintegrate.
      The purpose of this article is to inform "Treasure Seekers" readers how they can build an inexpensive electrolysis machine which will do a splendid job of cleaning coins or other small metal artifacts.
      The first thing you will need to obtain, if you don't already have one, is a 9 to 12 volt AC adaptor, often called an AC/DC convertor, or battery eliminator. This is the same electrical device which plugs into an electrical wall outlet and lets you operate portable radios, cassette players, and so forth, without the use of batteries.
      When choosing the AC adaptor for your mini electrolysis machine, take note of its rated output. This will be printed somewhere on the adaptor, and will usually be listed in milliamps (1/1000th of an ampere) which is designated by the symbol "mA," as in "350 mA." The higher the output, the faster the cleaning effect; I recommend the selection of an adaptor of at least 300 milliamp output.
      You will also need several small electrical "alligator clips," a stainless steel spoon, a non-metallic cup or small bowl, water, and some common table salt.
      To convert your AC adaptor into an electrolysis machine, first cut off the little plug device from the end of the wire. (The "plug" referred to here is the one that connects to the radio, cassette, etc., NOT the one that connects to the wall socket) Once you've removed that little plug, you will note that the wire to that little plug is a double-strand wire; beginning at the cut off tip, very carefully separate (pull apart) those two individual strands of insulated wire for a distance of about 6 inches, leaving the insulation intact on each of the wires. Next, strip away about a quarter to a half inch of insulation from the tip of one of those loose wires, and where the insulation has been removed firmly affix (crimp into place) an alligator clip. Be sure that there is a good electrical contact between the bare wire and the alligator clip. Now, repeat that procedure to the other strand of wire. You will now have two single-wire sections, each with its own alligator clip.
      Now, make up an ample supply of electrolyte solution, at the ratio of at least 1/2 teaspoon of common table salt for every 8 ounces of water. Pour some of this electrolyte solution into the cup, nearly filling it. Place both alligator clips into the solution, being careful not to let them touch one another. Remember, once we plug the adaptor into the wall socket, electrical current will be flowing to the alligator clips, and if they touch one another, the adaptor will short out, and be ruined.
      After you've made sure that the alligator clips are not in contact with each other, plug the adaptor into the wall socket, and watch to see which of the two alligator clips begins to produce bubbles. The one that begins to bubble is the cathode, or negative pole of the AC adaptor. The side that does not bubble is the anode, or positive electrode. Unplug the adaptor, remove the alligator clips from the solution, and in some way mark the polarity of the wires.
      Bend the stainless steel spoon into a sharp "U" shape so that, when hung over the lip of the cup, the "bowl" of the spoon can reach about half way deep into the cup.
      Hook the anode (positive, non-bubbling) alligator clip to the portion of the spoon which is outside the cup. Then, hook the cathode (negative, "bubble side") alligator clip to the object to be cleaned, and suspend it into the solution, over the edge of the cup opposite the spoon, and use one of your spare alligator clips (or a clothes pin, etc.) to secure that artifact-holding wire in place. You want to be sure that the object to be cleaned is fully immersed in the solution, and suspended more or less at the same level in the cup as the bowl of the spoon.
      Once that is done, you are now ready to begin the electrolysis cleaning of your artifact. Making sure that the two electrodes are not touching, plug the adaptor into the wall socket. Within moments, the object to be cleaned should start producing bubbles. If not, unplug the adaptor, and reposition the alligator clip on the artifact, preferably at a point where metal is showing. Then plug the adaptor back into the wall socket.
      Once the coin or artifact is merrily bubbling away, then everything has been done right. So what is taking place? During electrolysis, ions (atoms which either have an excess or deficiency of electrons, and thus are electrically charged) are liberated from the poles, and these migrate through the electrolyte solution to the oppositely charged pole. The cathode, to which the artifact is attached, is the point of entry of anions (negatively charged atoms with a surplus of electrons) into the electrolyte solution. The liberation of anions, from the chemical compounds which constitute the corrosion on our artifact, triggers chemical changes within those compounds, causing them to disintegrate into less complex chemical substances. Proof of these chemical changes are seen not only in the artifact becoming progressively more clean, but also in the discoloration of the electrolyte solution as dirt and various chemicals are released into it, as well as a build-up of "gunk" on the stainless steel spoon.
      How long does it take for an object to become clean? That depends on how badly it is corroded. After a few minutes, unplug the adaptor, remove the coin or artifact from the solution, and gently rub it with your fingers or a soft toothbrush to remove loosened corrosion, then rinse it thoroughly in clean water. If it is acceptably clean, then there is no further need for electrolysis. If it still needs further cleaning, return it to the solution, and resume electrolysis. This process may have to be repeated several times for badly corroded or heavily concreted objects. During this process, should the electrolyte solution become notably discolored, replace it with fresh solution.
      Several things should be kept in mind regarding electrolysis. First, it should be remembered that corrosion progressively affects the metal of the object, and in advanced stages of corrosion little or none of the original metal may be left; in other words, all that may be left is a lump of corrosion more or less resembling the original object. This is especially true if the object was made of thin metal to begin with, or if the metal was one that corrodes especially easily, such as tin, aluminum, etc. Sometimes, severely corroded objects will crumble away to nothing when submitted to electrolysis. Thus, you will have to make the decision whether submitting a particular object to electrolysis will likely be worthwhile.
      Also, don't be in too big a hurry to clean every object you recover. Keep in mind that cleaning off the layer of corrosion will merely reveal "what's left" of the object, and in some cases, that is not very impressive. If the object has reasonably good patina and is aesthetically pleasing, leave it "as is."
      A word of caution: from time to time, feel the AC adaptor to determine if it is getting too hot. If so, disconnect it, to let it cool off. Such overheating will occur as the artifact becomes progressively cleaner. This, in turn, allows for a greater flow of electrical current o pass through the adaptor, increasing its temperature. Thus, never leave your electrolysis machine on and unattended for any length of time.
      Careful use of your mini electrolysis machine will help transform many of those "ugly blobs of corrosion" into beautiful coins and relics.
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