Bill,

What kind of stone are they? Must be pretty solid to handle 1500 piss. 
Have you tried soaking them in a bath of water and then scrubbing at 
them? Suggest that you need to 1) identify what the stain is from 
(organic/mineral) and then 2) apply toilet paper poultices either with 
straight water and/or with appropriate solvents to dissolve the stain 
material. Make sure your water is clean of minerals. Discoloration from 
dunnage if it is rust stains (orange, or once orange and now black) you 
can try Iron Out that you can purchase in the plumbing section at Home 
Depot, it is essentially oxalic acid... be cautious and do not apply it 
too strongly... dilute and work up the concentration. Possibly 
experiment on sides not to be seen in the final installation. Often you 
can get the surface of a stain to clean off but there will remain a 
ghost where the stain material is into the stone and shows through. This 
is when you would use a poultice to dissolve and then suck the stain 
out. Use of acidic cleaners will not do very well, particularly if they 
are over concentrated, for a stain into the stone. Poultices may need to 
be repeated several times. Good luck... sometimes it never works.

Please say hello to family for us. Keep warm.
][<en

William Gould wrote:
> Advise please.  
>
> I need to clean an 18 century firebox that was removed from a building 
> and has laid outside for thirty plus years.  Some pieces laid face up, 
> others laid face down while other pieces laid atop others on dunnage. 
>   All are now face up. There is staining where the dunnage made 
> contact, some discoloration overall and the lintel that laid face up 
> has a black residue on a portion of it.  Same black found elsewhere on 
> other stones.  I tried a power washer, 1500 psi, Dawn detergent and 
> ammonia worked with a wire bush.  While the lichen and some of the 
> discoloration has been removed there is an obvious unevenness in the 
> look of the stones.  I should add that the cheeks are one piece as is 
> the lintel.  Photos emailed showing conditions upon request. -- To 
> terminate puerile preservation prattling among pals and the 
> uncoffee-ed, or to change your settings, go to: 
> http://listserv.icors.org/archives/bullamanka-pinheads.html 

--
To terminate puerile preservation prattling among pals and the
uncoffee-ed, or to change your settings, go to:
<http://listserv.icors.org/archives/bullamanka-pinheads.html>