No need to worry about verdigris and bluish water
Some think verdigris and bluish water are toxic. But that is not true at all.
In August 1984, the Ministry of Health and Welfare (current Ministry of Health, Labour and Welfare) acknowledged that the notion that verdigris is highly toxic was false.
Let us take a close look at verdigris and bluish water to gain a true understanding.
Misunderstandings about verdigris
Is verdigris highly toxic? That is a great misunderstanding.
It had been long believed “verdigris,” one of copper rust was toxic. The reason for this was not clear, but it is mainly thought that past statements in school textbooks may have been misleading.
Press articles about research findings released by the Ministry of Health and Welfare (current Ministry of Health, Labour and Welfare)
It was written in elementary school science textbooks used during the Showa era that verdigris, one of copper rust, is toxic. Similar statements were also found in the encyclopedias of that period. It appears that knowledge gained through those statements has been long believed.
To put an end to such misunderstandings and gain a more correct understanding about copper, the Japan Copper Development Association consulted the Faculty of Medicine, the University of Tokyo, and conducted experiments on animals in relation to verdigris over six years. As a result, it was confirmed that verdigris is a substance that is virtually not toxic.
Following this outcome, the Ministry of Health and Welfare (current Ministry of Health, Labour and Welfare) also initiated animal testing in 1981 as a national government research project. After three years of studies, the Ministry also concluded that verdigris was virtually not toxic. The study results spread across Japan via NHK news and newspapers.
Nonetheless, more than 30 years after the announcement from the Ministry of Health and Welfare, the notion that verdigris is toxic still remains. It is a desire of the Japan Copper Development Association that correct knowledge of copper and verdigris will be shared with all the people in Japan.
Color change over time
- Reference picture
Changes in color of copper over time create an appearance that suits the aesthetic sensibilities of the Japanese. The luster of a new copper plate diminishes in one month or so, and in general, the color changes gradually from reddish brown to patina color shown above.
As seen in the reference picture above, copper is used for roofs because of its durability and beautiful color. The roof of the Nikorai-do (Holy Resurrection Cathedral), located in Kanda, Tokyo, used to be reddish brown, but it gradually changed to a patina color over the period of a decade.
Let’s have accurate knowledge about bluish water
Some people observe that they got bluish water from a faucet. However, bluish-colored water does not come out from a general household faucet. If the water from the faucet appears bluish, you can easily confirm this by putting some water in a clear glass. The water will most likely be clear.
More than 100 ppm of copper ion needs to be blended into tap water to make the water look bluish. The standard amount of copper ion contained in the general household tap water is 1 ppm. For this reason, tap water cannot be bluish due to copper ion.
As shown in the picture on the right, you may have also seen a blue stain in the sink or bathtub where soap is used. This occurs due to insoluble copper soap generated when fatty acids present in soap and scale react with a tiny amount of copper ion. This is harmless. The stain can be completely removed with kitchen oil stain removing detergent.
When a copper pipe is new, copper ion in it is more easily dissolved into the water passing through the pipe, which triggers this phenomenon. However, as you continue to run cold or hot water, the inside of the copper pipe will build up cuprous oxide, preventing dissolution of the copper ion into the water as it passes through the pipe.
Why does the water in the bathtub look bluish?
The visible light, which is visible to the human eye, consists of rays of colors（red, orange, yellow, green, blue, indigo, and violet). When the red side becomes weaker, it appears more bluish, and when the violet side becomes weaker, it looks more reddish.
Clean water in the bathtub sometimes looks blue. This is because a small part of the energy of the longer wavelength (red) side is absorbed by the water and the material of the tub, resulting in an increase in the ratio of bluish light. This is supported by putting tap water in a clear (or whitish translucent) glass and an opaque glass. When observing these two glasses from above, the water in the opaque glass will appear bluish.