I know very little about these. Some titanium were made in a commerative motif to commerate some of the first postage stamps. I know Tom Maringer makes some pieces in Niobium , may be he could fill us in on the process as he knows it. Tom, have you ever thought about stick pins from some of your coins to add to the jewelery line ?
The "weird" metals The more unusual metals I've worked with have included Titanium, Niobium, Tantalum, Hafnium, and high-purity Iron. They have some unusual properties. Pure iron is a completely different animal than steel... which is an alloy of iron with carbon. The pure iron I was getting had a carbon content less than 0.002%. At that level iron is a little softer than copper, and does not work harden hardly at all. It will just keep working and working, almost like pure gold. The other 'transition" metals tend to be harder to strike than copper or silver... and a bit 'smeary'... that is... they tend to leave smears of metal on the dies if there is too much flow across the surface. For this reason they are best used on low-relief pieces with minimal flow. Also the hardness of the metals will break down or wear dies two to three times as fast as usual... so I have generally done only short runs with them. They are a bit costly and impossible to weld or smelt. So any scraps are not recyclable usiung ordinary methods. Pure iron is awesome stuff... but terribly hard to get and costs three four times what copper does. The mill that used to make it in Germany has apparently closed, and I managed to get a few pounds of the last stuff... I used it for my "Iron Crown of Morgoth" It takes detail extremely well and looks really cool when "blued" a deep black. The only problem is that people expect iron to be cheap. Iron is NOT the same thing as steel, and I sometimes get tired of explaining it. Titanium is the easiest to get, and very light, but the finish on the plates of the high-purity grade-1 is a terrible orange-peel. Unless you have them ground flat (very expensive) you have to coarse-tumble the blanks for WEEKS to get them smooth enough to strike, and even the high-purity grade is hard on dies. Hafnium is even harder to strike than titanium... but it is denser than silver and takes GORGEOUS anodization colors, especially green. It's particularly interesting stuff because of its nuclear properties (it is the best neutron absorber of all... and makes great radiation armor) Tantalum is a very dark gray metal and nearly as dense as gold (black-gold?). It runs three to four times the price of silver... and tough to locate at any price, but has the deepest blues and purples in its anodization range. Niobium is perhaps the most interesting and forgiving of all these transition metals. It's about the same density and hardness as copper, coins pretty well and has a wide range of nice anodization colors available. The problem with niobium is availability, dimension, and price. Most of the stuff is 0.040" or thinner... which is pushing the lower limits of what we can use for minting and it costs about the same as silver... but you can't recycle the blanking scraps, so there is lots of waste. All of these metals have the property of extremely high melting points and are highly reactive with oxygen at elevated temperatures. I've made buttons and lapel pins out of many of my coin designs using copper brass and silver... but in niobium the stick-pin idea would be tough because of its properties... you'd probaly have to use a laser or perhaps a spark-welder to put a post on the back. It might be possible to make some sort of mechanical connection with rivets or pins.
Have to agree that was very interesting specialy as I have a few Titanium coins in my collection, it sort of brought them to life a bit more Thanks Tom :bow: De Orc :bow:
Yes! And those Austrian coins look very good. I'd love to pick some brains of the guys that worked out the technical details on those.
Extreamly educational. However, one thing left out that should be noted is what are the Oxydation reations with these metals. For example pure Iron should Oxydise rather rapidly. Same with most raw materials. Even metals like Gold and Platinum can Oxydise. What happens to many of the other metals noted when exposed to moist air and CO2? Or are these products coated?
Hi Tom, yep very educational! may I ask how do you anodize (process) and get the different colors? Is it easy to get the color so evenly on the coins? I have seen the purple Austria coin (2005) and I must say its one of the most amazing colors I have ever seen on a metal...
Oxidation on iron is usually called rust. It is NOT considered desirable because the iron oxide is generally not strongly adherent... that is... it flakes off easily and therefore craters out the surface... bad. But the good thing is that pure iron rusts much less than steel does! The idea is to "blue" the iron. I either heat-blue the coins in a pan on the stove (which gives a deep purple-black) or else take them to a gunsmith to be hot-blued chemically (which gives a flat-black). Either way, I then do a coat of paste-wax on the coin to help prevent rust. Even so... sometimes it happens. Anodizing is another form of oxidation! In the cast of the reactive transition metals (Ti, Ta, Nb, Hf) the oxide skin is both adherent and transparent. The most common method is to form an oxide layer by electrolytic means, similar to the process used in electroplating. The work to be colored is attached to the positive connection of a power supply (the anode), and usually another piece of titanium is connected to the negative side (the cathode) of the supply. Both are submerged in a mildly conductive solution, such as phosphoric acid (cola soft drinks), TSP - TriSodium Phosphate (dishwasher detergent). When power is applied to the contacts, a uniform layer of titanium oxide forms on the anode. As the voltage increases, the thickness of the layer also increases. Certain colors will appear at specific voltage levels. The "change" from one color to another is not sharply defined, but rather shades gradually through a limited spectrum. The colors are interference colors... like the colors you see in an oil-slick. The apparent color imparted to the metal is caused by interference between certain wavelengths of light reflecting off the metal and oxide coated surface. Light passing through the oxide layer, then reflecting off of the metal, must travel farther than light reflecting directly off the surface of the oxide. If one wave pattern is out of synch with the other, they will cancel each other out, making that particular color "darker" or not visible at all. If the thickness is such that a specific wavelength of light following one path closely synchronizes with that of the other path, then the wave strength (amplitude) will be increased, and that particular color would appear brighter. When the wave patterns cancel each other, it is called destructive interference, and when they match, it is constructive interference. It is possible that the thickness will create a combination of effects at the same time. The thickness of the coating is controlled by the voltage settings in the anodizing process. Each metal or alloy has its own specific color range at different voltages... so you need to calibrate for the target color for each different metal. But the results are generally repeatable if other factors are kept constant. The colors on the Austrian niobium coins should be quite durable... but wear can reduce the thickness of the oxide layer, and thus alter the color. You can actually use very fine polishing compound and blend colors by careful rubbing!
No idea which countries issue "medal-coins" but Austria's Millennium coins for example (100 Schilling "Communication" 2000, 100 S "Mobility" 2001) are silver/titanium pieces: The pill (middle part) is Titanium, the ring is silver. After the cash changeover, the silver/niobium coin series followed the Ti issues, with the pill in different colors: 2003 - Hall in Tirol (blue) 2004 - Semmering Railway (green) 2005 - Television (purple) 2006 - Satellite Navigation (brown) 2007 - Aviation (turquoise) The latter will officially be issued on 28 February. Christian
Wow, thanks Tom. Didn't realize that they were interference colors! Nice to know. I assume the oxides are non-conducting so the voltage applied set point limits the thickness of the layer. Maybe I could try it once myself... You once made coins in halfnium (Blood of S'urak) and tantalum I see... but they are not available anymore.. are there any future plans of remaking these? Aidan, the Pobjoy Mint started making coins in Titanium back in 1999... purely collectors items. The Gibraltar Millennium issue (5 pounds) was a silver colored coin (can get one on eBay for about $40 or so)... awesome to handle, they are incredibly light even though they seem to be the size of a normal 1 oz. silver bullion coin. They issued blue and red versions later (to commemorate stamps). Recently they have started making bimetals with Titanium/silver and titanium/gold. They had once stated in some newsletter that its tough to make blanks (as Tom mentions above) and the metal would kill the die about 100 times faster than silver so one should never expect titanium to be in circulating coins in the future...
Aiden I will repost mine in a while so that you can have a look £5 1999/00 Millenium 2000 Titanium 2p Blue,160th Aniversary uniform penny post $5 2004 Titanium 2p Red British Guiana (Worlds Rarest Stamp) 2005 Titanium 4p Green Inverted Swan (Western Australia) De Orc
Indeed. The best one in that series was the first issue (Hall) IMO, first because it was blue and also due to the design. One side features a Tyrolean Guldiner coin, or rather its die, from the Hall mint. http://www.austrian-mint.com/bimetallmuenzen?muenzeSubTypeId=113&muenzeId=216 Last year's color was ho-hum, but the 2007 issue is fine with me again: http://www.austrian-mint.com/bimetallmuenzen?muenzeSubTypeId=113&muenzeId=562 Christian
