I am not any help but there is a post somewhere about rust! I have read it. Keep looking for info and call a tile company in your area to see if you can find an answer. Or email Dal Tile; they are a big company and may be able to help you.

I have never heard of this before; If the installation would have failed ( waterproofing issue) then you would see it on all parts of the tile not just the edges and what is really weird is if you are seeing this and haven't used water on it maybe the tile is defective? I would suggest contacting the manufacturer of the product and see what they say.

Try the guys over at the John Bridge Tile forum. I think they have seen just about everything. Post pics over there if you can.

http://www.johnbridge.com/vbulletin/forumdisplay.php?f=1

I would definitely get hold of the tile manufacturers and see what they can do.

what was under the tiles? Did they just use hardibackerboard (not waterproof) or did they use a complete waterproofing system or chicken wire with stucco/smooth coat underneath for a waterproof application?

Your picture to send the maker will have to be much better to be honest i can’t even see what you are talking about, but i would be asking exactly what was done in the install from start to finish and record the conversation just in case you find out later something did not get done right.

That picture is no help at all.

Take a picture of each stain standing about 12" away so the stain can actually be seen in the photo. And do it with some reasonable lighting in the room

Is your tile from Italy? I know some people who had similar issues and they found out that the marble was from China..it had something to do with the way it was produced, etc..

There used to be an author on this site that addressed this specifically. It appears that his comments have been removed from similar questions regarding tile issues. His idea books are still here though. Link for two that you might find helpful. Good luck with this.

[https://www.houzz.com/magazine/convert-your-tub-space-into-a-shower-waterproofing-and-drainage-stsetivw-vs~8573824[(https://www.houzz.com/magazine/convert-your-tub-space-into-a-shower-waterproofing-and-drainage-stsetivw-vs~8573824)

[https://www.houzz.com/magazine/why-marble-might-be-wrong-for-your-bathroom-stsetivw-vs~12133357[(https://www.houzz.com/magazine/why-marble-might-be-wrong-for-your-bathroom-stsetivw-vs~12133357)

We have seen a lot of dilemmas posted on Houzz over the years about rust stains coming out in marble. It happens in slabs so I don't know why it wouldn't happen in tiles as well. Do a search here on Houzz for marble stains and see if there is advice/information that might be helpful.

Rust on Carrara marble tiles comes from iron deposits within the stone. I had an entire bathroom done in Carrara marble tiles back in 2003. It was great for a while, but then stains started to “bloom” on the surface. And, to make it worse, stains appeared at the top of the shower enclosure which was never really wet, so high humidity will even cause the discoloration. I could do nothing to eliminating the stains, however, I resorted to “painting” the spots with a mixture of white and gray artist paint, and believe it or not, it helped.

I am going to do a new bathroom soon in another apartment, and so I will use ceramic tiles that look like real Carrara marble, and I know they are available.

Fred Houston, a stone consultant, wrote a column on how an entire marble floor had to be removed because the client was too cheap to keep the air conditioning on during construction. The ensuing humidity rusted the floor. If the humidity in the air can rust marble, imagine what the humidity in a shower will do. Tear it out or learn to decorate with orange.