We have a well that delivers hard water and we do not have a water softener. (There was a “green sand filter” that utilizes permanganate to oxidize other metals on the system, but it has been disconnected.) Analysis of the well water shows the presence of iron in noticeable amounts. No other metal ions were specifically identified. The system does have an ozonator to oxidize Fe(II) to Fe(III). Over the last couple of years, the porcelain toilet bowls have developed a blue ring at the air/water interface. When you scrub on the blue ring, it doesn’t feel like there is a deposit present (like normal hard water deposits). The ring is unresponsive to ammonia (household), strong acid (6 M HCl) or strong base (Drano), as well as to hydrogen peroxide (30 %). (We haven’t tried a good reducing agent yet.) So, my question is, does anyone have an idea of what is causing the blue color? Is it possible that porcelain reacted chemically with salts, urea, uric acid, oxygen, etc? Not an earth-shattering theoretical question, but I’m chemically curious as to what this could be if anyone has any ideas.

  • $\begingroup$ I know this may seem silly...but I've spent several hours looking up information on colored salts, colored complexes, and trying to find out some information about the reactivity of porcelain and nothing has been useful. And the site has been asking for more questions..... $\endgroup$ May 11, 2012 at 5:15
  • $\begingroup$ are you in NC or Georgia? $\endgroup$
    – Chris
    May 11, 2012 at 10:34
  • $\begingroup$ I'm actually in California. $\endgroup$ May 11, 2012 at 15:07
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    $\begingroup$ The blue color is copper from some copper or brass plumbing, presumably. The "bulk" of the deposit is SiO2 (hydrated), doped by Copper. $\endgroup$
    – Georg
    May 15, 2012 at 12:52
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    $\begingroup$ I second the idea that the blue is from copper. What part of California do you live in Janice, the Valley? Very hard water around there. $\endgroup$
    – Pat
    May 16, 2012 at 1:49

2 Answers 2


Toilet bowls are made of ceramics which can contain feldspar. Toilet bowls also often have a feldspar glaze. There is a study that disolved Cr(VI) can be removed by feldspar.

Studies on the removal of Cr(VI) from waste-water by feldspar http://onlinelibrary.wiley.com/doi/10.1002/jctb.280530204/abstract

The IMA currently recognizes 90 Cr bearing minerals. 16 minerals if you only count those that contain also Si. Feldspar can be either K, Na or Ca-Feldspar. Of those 16 minerals 6 contain Na, 2 K and 5 Ca. Reading those papers might even narrow the choices down to a couple of minerals that can form in standard-toilet-bowl-conditions.

Mineral database that lets you select minerals by their chemistry: http://rruff.info/ima/

I think that unless you are willing to donate your toilet bowl to science that the answer won't get any more precise than this.

Edit: Cu would be the favorite choice for a blue color mineral (Azurite, ...). There is also a study about the removal of copper by feldspar:

Experimental studies of the interaction of aqueous metal cations with mineral substrates: Lead, cadmium, and copper with perthitic feldspar, muscovite, and biotite http://www.sciencedirect.com/science/article/pii/S0016703797001178

Again there are 603 Cu-minerals. Cu+Si=32 minerals. With the common Feldspar cations your left with about 10 each. I don't think the minerals could be recognized visually. The favorite method would be x-ray diffraction of a powder sample of the blue stuff.

  • $\begingroup$ Thanks for the information..now I need to take some time to go through it. It would be nice if there were some simple solubility tests to ascertain whether this approach has merit...without sacrificing the toilet bowl to science. (Although maybe when redecorating time rolls around....) An interesting idea, at any rate. $\endgroup$ Sep 13, 2012 at 3:47
  • $\begingroup$ XRD of a glaze will not yield any results as glazes are glasses, not crystalline. $\endgroup$
    – A.K.
    May 22, 2016 at 5:02

I heard it is a high acid content in the water which is eating away at by he copper pipes. The copper turns blue when oxidized like the statue of liberty, the copper residue stains the toilet bowel. This was very rare until fracking started.

  • $\begingroup$ Oxidized to what? Are you saying it's copper(II) sulfate pentahydrate? $\endgroup$
    – M.A.R.
    May 25, 2016 at 19:04

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