Yes-we do a good amount of these-before you commit to any process-do some testing-
While I generally go right to the abrasives-in this case custom cut DIP's or sandpaper used with a sponge, anything that will get you into the angles and form of the surface.
While it will give you a clue to how deep the staining is you will have to be able to blend in and match the finish.
So I think the best approach is to use a combination of techniques .
Creosote is grease-prosoco makes a fireplace cleaner-https://prosoco.com/Content/Documents/Product/SK_Fireplace_Cleaner_PDS_110311_C.pdf
You could use MB-2 as well its 12.5 ph-we place paper towels on the stone and spray MB-2 onto the towels-they will stick nicely.** Protect areas from dripping product.
Leave on for an hour or two then remove scrub and rinse.repeat if needed.
You could do a poultice(http://www.mbstonepro.com/stain-reaper/) but takes forever.

On Thu, Feb 15, 2018 at 9:13 AM, Fred Hueston <fhueston@gmail.com> wrote:
Stu may have something similar too. check with him

On Thu, Feb 15, 2018 at 9:12 AM, Fred Hueston <fhueston@gmail.com> wrote:
I have good luck with Prosoco Liquid marble cleaner...Give that a try

2018-02-15 7:20 GMT-05:00 Stuart Young <santafefc@sbcglobal.net>:

The limestone around this fireplace is dirty from soot. Our conventional methods of cleaning had little or no effect. Any ideas on hot to clean this stuff. Homeowner wants it to look lighter. All the curves do not help the situation.Stuart Santa Fe Floor Care
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Frederick M. Hueston
www.stoneforensics.com
office             321 514 6845      
Stone Inspection and Troubleshooting seminar June 11-14, Melbounre FL
For more details see the training section at www.stoneforensics.com
check out the Stone and Tile Radio Show at http://www.blogtalkradio.com/drfred







--
Frederick M. Hueston
www.stoneforensics.com
office             321 514 6845      
Stone Inspection and Troubleshooting seminar June 11-14, Melbounre FL
For more details see the training section at www.stoneforensics.com
check out the Stone and Tile Radio Show at http://www.blogtalkradio.com/drfred




 
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Regards,
Stu Rosen
201-446-1200