This beautiful surface of golden brown coloration is the result of very delicate work as shown below.

1. A single copper sheet is hammered into shape and then cleaned to remove any oil or other contaminants. 
2. Soaked in a sulfurizing solution to form an artificial rust coating.
3. Next, the black rust is polished off from the entire surface of the sake cup, taking into consideration the design and coloring of each piece. The black color is left only on the hammered surface to accentuate the shading.
4. Finally, the piece is soaked in boiling color solution made by traditional technique to develop a golden-brown color.

The color is brighter than that of ordinary sulfurized brown copper. As it is carefully used, it becomes more austere and atmospheric, and its color develops into a deeper hue.

Seigado has a workshop at the foot of Mt. Yahiko in Niigata Prefecture, where high quality copper was discovered about 300 years ago and "Tsuiki'', the technique of hammering copperware has developed since then.

"Tsuiki'' is a metalworking technique that is derived from the words 'hammer' and 'raise', so this process literally means hammering and embossing copperware products. The traces of the hammering, the process of making are left as beautiful patterns on the products.