AT Question - Can coins other than Niobium, Titanium or Aluminum be anodized to produce colors?
MrSpud
Posts: 4,499 ✭✭✭
I was looking up info about how those Niobium coins from Latvia and Australia are toned different colors by their countries mints (see the following like for details Link to Niobium Thread ) . They do it through a process called anodization. Well anyways, I stumbled across this information on a reactive metals site Reactive Metals Site and was wondering if this can be done to coins made of other metals. Like maybe this is how some Doctors do it to make them look better than the easy baked ones. Or would anodization only work on metals that end in the letters UM? Anyways, read this passage and let me know what you think. The passage starts off with a general talk on coloring and says that there are 2 ways to do it, thermal oxidation and electrical anodizing. I know you can thermally oxidize coins and I have attached a picture of a nickel that I thermally oxidized myself. The picture is at the bottom of the page and is a cut and paste collage of the same coin taken every 8-10 seconds as it went through the color changes as I thermally oxidized it. This makes me wonder if regular coins can be anodized electrically? Anybody know?
"Coloring
Coloring can be achieved in two ways; thermal oxidation and electrolytic oxidation (anodizing). Both processes do essentially the same thing. Through electron excitation, the metals react with oxygen to form a thin transparent film. Thermal oxidation (heat coloring) is simple, but difficult to control. Anodizing is infinitely more predictable and is the only effective way to color niobium.
The colors produced appear in up to five repeating orders. Most of the current jewelry is produced with the first two orders. All the colors of the light spectrum are not produced. True red and forest green are not generated.
When the oxide is of a thickness to generate interference colors, its depth is measured in angstroms (Å=1/100,000,000 centimeter). This layer can vary in thickness from 500 to 1,000Å+ depending on the color. It is not the oxide itself that is perceived by the viewer but its effect on light.
Although harder than the parent metal, the extreme thinness of this oxide dictates that it is not a strong wearing surface. Bracelets, belt buckles, rings and items that normally receive heavy abrasion should not be considered unless the metals are protected by other design elements."
"Anodizing
Anodizing most closely resembles standard electroplating. When a reactive metal is suspended in a electrolytic bath as an anode(+) and current is passed through the bath, oxygen is produced at the anode surface. This oxygen reacts with the metal to form a thin oxide film that generates colors. The transparent oxide increases in thickness in relation to the amount of voltage applied. At any given voltage the oxide will grow to a specific thickness (i.e. color) and stop, having reached a stage where current will no longer pass. This phenomenon of voltage controlled growth means that the color is also voltage controlled.
An area of oxide produced with a high voltage will not pass current from a lower voltage. In other words an area anodized at 60 volts will not need masking when an adjacent area is anodized to 40 volts. It follows that multiple anodizing processes should proceed in decreasing voltages. Working in descending order will save masking and generate fewer errors.
While oxygen is generated at the anode(+), hydrogen is formed at the cathode(-). Titanium and stainless steel make most convenient cathodes. This process does not have much throwing power and it is necessary to have a cathode equal to or larger than the anode.
The electrolytic solution can be almost any liquid capable of carrying current. Such diverse solutions as Coca-Cola, Sparex, sulfuric acid, ammonium sulfate (fertilizer), magnesium sulfate (Epsom salts), trisodium phosphate, dish detergents and even wine will work. Recommended here is a solution of 3 to 10% by weight trisodium phosphate (T.S.P.) in solution with distilled water. The percentage of chemicals in the solution will determine to some extent the length of time for the desired reaction to be completed. Slowing the reaction can be achieved by lowering the concentration of chemical in solution.
Power supplies
The power supply required for anodizing has a much greater range of voltage control and lower range of current capabilities than plating rectifiers. The requirements are 0-150 volts DC variable in one volt increments and from 2-5 amps. Larger capacity power supplies may be necessary for work larger than jewelry and in high volume production.
Anodic painting
Note: The metal ferrule of paint brushes, other metals and conductive materials that could come in contact with the operator or cause a short circuit should be covered with electrical tape or coated with a plastic coating. Always wear rubber gloves.
This is where the real graphic potential of this process comes into play. This technique brings the electrolyte to the work. Applicators can be made by soldering an insulated wire on to the metal ferrule of an artist's brush or clipping on to a sponge with the cathode lead wire.
Connect the anode(+) lead from the power supply to a reactive metal workpiece. Connect your applicator to the cathode(-) output of the power supply. Moisten the applicator in electrolyte. Turn on the power supply and set the voltage to the desired level. Touch the applicator to the surface and the colors will begin to appear.
Applicators
If the applicator is held in one position the colors will slowly radiate out from the point of contact. With excess electrolyte and constant movement, even large areas can be evenly colored. Fine detail work can be produced with an almost dry brush.
How to Rainbow Anodize
Rainbows are intoxicating! They are so beautiful to look at that it is almost impossible not to indulge yourself and make a few. Rainbows can be worn in any season with any color and for any occassion. They are always in fashion! The can be as simple as two color as complicated as double rainbows emanating from a central point. They are easy and fast.
Here is what you do for a single rainbow progressing from one end of the piece to the other:
1) Hang the piece from a submersible hook like the MINI Grabber or with a fine niobium or titanium wire if it has a hole in it.
2) With the voltage turned down to zero completely submerge the piece in your electrolyte.
3) Slowly turn the voltage up until the color you want to start with appears.
4) Slowly lift the piece out of the electrolyte while you continue to turn up the voltage. Just like that you have a rainbow! It will take some practice to get the colors to flow just the way you want. It is best to anodize pairs together. No two will ever be just alike.
Here is what you do for a couble rainbow progressing from the center to the ends: Repeat steps 1, 2 and 3 above to set a base color.
4) Lift the piece partially out of the electrolyte and then continue to make the rainbow.
5) Once you have anodized the first half, turn the piece over and submerge it half way again and repeat the rainbow process."
"Coloring
Coloring can be achieved in two ways; thermal oxidation and electrolytic oxidation (anodizing). Both processes do essentially the same thing. Through electron excitation, the metals react with oxygen to form a thin transparent film. Thermal oxidation (heat coloring) is simple, but difficult to control. Anodizing is infinitely more predictable and is the only effective way to color niobium.
The colors produced appear in up to five repeating orders. Most of the current jewelry is produced with the first two orders. All the colors of the light spectrum are not produced. True red and forest green are not generated.
When the oxide is of a thickness to generate interference colors, its depth is measured in angstroms (Å=1/100,000,000 centimeter). This layer can vary in thickness from 500 to 1,000Å+ depending on the color. It is not the oxide itself that is perceived by the viewer but its effect on light.
Although harder than the parent metal, the extreme thinness of this oxide dictates that it is not a strong wearing surface. Bracelets, belt buckles, rings and items that normally receive heavy abrasion should not be considered unless the metals are protected by other design elements."
"Anodizing
Anodizing most closely resembles standard electroplating. When a reactive metal is suspended in a electrolytic bath as an anode(+) and current is passed through the bath, oxygen is produced at the anode surface. This oxygen reacts with the metal to form a thin oxide film that generates colors. The transparent oxide increases in thickness in relation to the amount of voltage applied. At any given voltage the oxide will grow to a specific thickness (i.e. color) and stop, having reached a stage where current will no longer pass. This phenomenon of voltage controlled growth means that the color is also voltage controlled.
An area of oxide produced with a high voltage will not pass current from a lower voltage. In other words an area anodized at 60 volts will not need masking when an adjacent area is anodized to 40 volts. It follows that multiple anodizing processes should proceed in decreasing voltages. Working in descending order will save masking and generate fewer errors.
While oxygen is generated at the anode(+), hydrogen is formed at the cathode(-). Titanium and stainless steel make most convenient cathodes. This process does not have much throwing power and it is necessary to have a cathode equal to or larger than the anode.
The electrolytic solution can be almost any liquid capable of carrying current. Such diverse solutions as Coca-Cola, Sparex, sulfuric acid, ammonium sulfate (fertilizer), magnesium sulfate (Epsom salts), trisodium phosphate, dish detergents and even wine will work. Recommended here is a solution of 3 to 10% by weight trisodium phosphate (T.S.P.) in solution with distilled water. The percentage of chemicals in the solution will determine to some extent the length of time for the desired reaction to be completed. Slowing the reaction can be achieved by lowering the concentration of chemical in solution.
Power supplies
The power supply required for anodizing has a much greater range of voltage control and lower range of current capabilities than plating rectifiers. The requirements are 0-150 volts DC variable in one volt increments and from 2-5 amps. Larger capacity power supplies may be necessary for work larger than jewelry and in high volume production.
Anodic painting
Note: The metal ferrule of paint brushes, other metals and conductive materials that could come in contact with the operator or cause a short circuit should be covered with electrical tape or coated with a plastic coating. Always wear rubber gloves.
This is where the real graphic potential of this process comes into play. This technique brings the electrolyte to the work. Applicators can be made by soldering an insulated wire on to the metal ferrule of an artist's brush or clipping on to a sponge with the cathode lead wire.
Connect the anode(+) lead from the power supply to a reactive metal workpiece. Connect your applicator to the cathode(-) output of the power supply. Moisten the applicator in electrolyte. Turn on the power supply and set the voltage to the desired level. Touch the applicator to the surface and the colors will begin to appear.
Applicators
If the applicator is held in one position the colors will slowly radiate out from the point of contact. With excess electrolyte and constant movement, even large areas can be evenly colored. Fine detail work can be produced with an almost dry brush.
How to Rainbow Anodize
Rainbows are intoxicating! They are so beautiful to look at that it is almost impossible not to indulge yourself and make a few. Rainbows can be worn in any season with any color and for any occassion. They are always in fashion! The can be as simple as two color as complicated as double rainbows emanating from a central point. They are easy and fast.
Here is what you do for a single rainbow progressing from one end of the piece to the other:
1) Hang the piece from a submersible hook like the MINI Grabber or with a fine niobium or titanium wire if it has a hole in it.
2) With the voltage turned down to zero completely submerge the piece in your electrolyte.
3) Slowly turn the voltage up until the color you want to start with appears.
4) Slowly lift the piece out of the electrolyte while you continue to turn up the voltage. Just like that you have a rainbow! It will take some practice to get the colors to flow just the way you want. It is best to anodize pairs together. No two will ever be just alike.
Here is what you do for a couble rainbow progressing from the center to the ends: Repeat steps 1, 2 and 3 above to set a base color.
4) Lift the piece partially out of the electrolyte and then continue to make the rainbow.
5) Once you have anodized the first half, turn the piece over and submerge it half way again and repeat the rainbow process."
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