Chemical coloring on the surface of the stainless steel is a technology of forming the acid hard film by putting the stainless steel in oxydant liquid (H₂SO₄-Cr₂O₃), thereby controlling the thickness of the film to create colors such as brown, gold, red, blue, green and black. So the chemical colors of the stainless steel are not those made by painting or technology of dyes but the natural color of the metals. It is inevitably affected by the materials largely since it is a method of natural coloring. So it is quite difficult to keep the reproducibility and, most of all, the management of materials is more important than any other things.
1) Management of Ordered Lot Generally, the materials are managed from the stage of purchase to input the same standard size of material for production and the same lot is put into the chemical tank after the test piece is inserted. After a certain period of time passes, it is judged whether the product has the same color as the sample and then put into the hardening tank for hardening of the surface. And then it is sent for neutralization treatment. Therefore, orders need to be made in a same lot since there would be some problems in reproducibility if the ordered sizes are different or the period of orders are different.
2) Etching Coloring If a product made through chemical etching is processed through chemical coloring, the coloring of the etched surface are also influenced. Therefore, it is required that the design should be done so that the etching space is not too broad. Beside, the surface of etching is needle phase and the color could be dark and uneven. So this should be taken into consideration as well.
3) Finger Mark Colored surfaces, if seen through a microscope, are similar to the volcanic rocks with many holes. So, the colors could change due to the interference effect of light when fingerprints are left, which are not removed easily. In order to keep the beautiful state, the products should be coated with a thin layer.
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