Do the hot bending toughened film with graphite mould. How do you deal with the pressure on the surface?
The easiest way to make coins naturally produce an oxide layer is to put clean, fat free coins into 10% of two sulfite solution for 10 to 20 seconds. Rinse off and dry with a soft cloth. Even after soaking two sulfite solution before copper will be issued a delightful bronze luster, and generally will not be corroded.
The cleaned copper seems less natural. With the passage of time, still will be black and the re emergence of copper oxide layer. However, we still can not guarantee that the new copper oxide layer will generate uniform, black spots appear not coin surface. So, the best cleaning copper oxide layers of naturally generated antique, give a person with the old feeling.
The cleaning process is as follows: pour nitric acid into the glass and prepare the soda water. The coin is quickly dissolved by placing it in the nitric acid solution with tweezers. Once the coin has been cleaned, clip the coins into the soda water with tweezers immediately. Then you can take the coins with your hands, rinse them with warm water and dry them. We need to point out that the nitrate in removing the oxide at the same time, also make the coin surface becomes little ma.
Do not use strong sulfuric acid or nitric acid cleaning solution of copper and silver. The solution washes away the oxide but also destroys the coins themselves, especially the subtle part of the coin pattern.
If the bronze coins and copper nickel coins corrosion (coin surface has a uniform black, dark green or black thick oxide layer), then it can be washed with strong sulfuric acid or nitric acid solution. Of course, this method of cleaning is only for coins that are not particularly valuable.
