Niiro Coloring（Patina coloring, Boiled coloring)

In this technique, copper or copper alloy is put into a solution of dissolved copper sulfate and patina, and boiled in the chemical solution to form an oxide film on the surface to add weather resistance and create a uniquely colored surface. The metal made by boiled and colored Shibuichi is sometimes called Rohgin or Oborogin.

Traditional Japanese Techniques

Baseplate Preparation	Cutting, forming process	Forming process	Polishing process
Prepare Shibuichi silver base plates. Originally, it was an alloy composition peculiar to Japan in which 75% of copper and 25% of silver were mixed, but the ratio of silver is low in modern Shibuichi products. The base plate includes 1% gold in a silver-copper alloy called shibuichi silver yaki (yaki means gold).	After measuring the size of the product, the base plate cut off in the appropriate sizes is prepared according to the shape of the product. Bend angles are adjusted little by little while heating the fixed base plate with a burner.	After the handle and scabbard base plates are heated and formed in a proper shape, details are checked and adjusted in accordance with the actual product. Accurately bend the curve, top, and bottom.	Apply charcoal powder or carborundum to a wet brush or cotton cloth to polish the surface to be colored. The amount of time it takes to grind and polish a piece varies depending on the size and shape of the product, but it takes at least several hours.

Mirror polishing process	Boiled-coloring liquid	Equipments used	Coloring method
After polishing the surface to a mirror finish, thoroughly degrease with baking soda. The accuracy of the degreasing treatment before coloring often affects about 70% of the finished coloring state. It is said that it's better to use grated radish on the surface before coloring, but this thought varies depending on the artist.	The raw materials used in the Niiro-coloring solution are patina, copper sulfate, and water. The proportion of each compound is not consistent. It is said that the standard ratio of boiling Shibuichi- silver is about 5.0g of patina and 3.5g of copper sulfate per 2L of water, but the ratio varies considerably depending on the desired color of the product.	The Niiro-coloring pot has to be made of copper that has not been plated. In addition, the boiling container has to be a basket made of bamboo that has not been coated. The handle has to also be made of copper wire.	Boil the Niiro-coloring liquid and let it cool down before the surface of the Shibuichi silver plate has become a mirror state. Put in the liquid and heat it to boil. This will gradually color it.

Coloring process	Finishing process	Color fixing	Attaching colored base plate
BGM Playing
To prevent precipitation of the raw material for the Niiro liquid during heating, it is necessary to constantly shake the basket in the pot up and down. After about 5 minutes from the start of coloring, remove the piece from the Niiro liquid and check the coloring state, but since the surface of the piece dries quickly, cool it immediately with water to prevent drying. Failure to do so may cause discoloration and unevenness.	Coloring is completed after about 30 minutes to 1 hour of boiling while checking the coloring state several times. After coloring the desired color, gently neutralize the surface with baking soda. Then lightly dry with a soft cloth or hair dryer.	Originally, after coloring, beeswax or wax privet was applied to the surface of the product to fix the color, but in recent years, clear car wax or lacquer is sometimes sprayed lightly to fix the color.	After confirming that the fixed color is completely dry, adjust the metal fittings of the Tachi koshirae. Tachi Koshirae with Niiro color finish here

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