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 currently named “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
The Myth That Verdigris Is High Toxic
It had long been believed that “verdigris,” one of copper's oxide 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
It was written in elementary school science textbooks used during the Showa era that verdigris, one of copper's oxides, is toxic. Similar statements were also found in the encyclopedias of that period. It appears that this myth has long been believed.
To put an end to such misunderstandings and gain a more correct understanding about copper, Japan Copper Development Association consulted the Faculty of Medicine, 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 has virtually no toxicity whatsoever at all.
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 without any toxicity. The study results spread across Japan via NHK news and newspapers.
Nevertheless, more than 30 years after the announcement from the Ministry of Health and Welfare, the notion that verdigris is toxic still remains. It is the desire of Japan Copper Development Association that the correct information about copper and verdigris be shared with everyone in Japan.
Color Change over Time
- Reference picture
Changes in the 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 the 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.
The Truth About “Blue Water”
Some people notice that the water from their faucet appears bluish. However, normal household faucets do not give bluish water. If the water from the faucet appears bluish, you can easily check this by putting some water in a clear glass. The water should be clear.
It takes more than 100 ppm of copper ion make tap water look bluish, but general household tap water limited to only 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 hot or cold 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 Buish?
Light visible to human eye is a spectrum containing different colors（red, orange, yellow, green, blue, indigo, and violet). When the red side of the spectrum 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 demonstrated 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.