It could be mineral deposits from the leeching from the rout joints and will razor blade off. Then you could hit it with a small 80 grit brush, and blend it in. It could also be etching. The marks seem to be either on top, or etches. Either way you can use the same techniques. 

On 16 Jan 2016, at 12:53 pm, Pat Staples <cpstaples@msn.com> wrote:

Looks like etching to me, since the lettering is probably painted on the panels I would just recommend you hitting it with some color enhancer



Happy Connecting. Sent from my Sprint Samsung Galaxy S® 5


-------- Original message --------
From: Tony Warney <tony@excelstoneandtilecare.com>
Date: 01/15/2016 9:29 PM (GMT-05:00)
To: sccpartners@stoneandtilepros.simplelists.com
Subject: travertine staining

Looking for some  ideas that are not to aggressive for removing these stains.

--
Tony Warney
Excel Stone and Tile Care
760-788-9400
 
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