Someone gave me some rocks but there were invasive vines on them that they tried to burn to kill. The rocks now have black charred places on them. I tried just plain water of course, but that would be too easy... I thought of vinegar? baking soda? or? I don't want to do anything too drastic and take off the patina/color of the rock (it isnt burned all over, just patchy) and some of the rocks have lichens on them that look like they could still be alive. Anyone with ideas?

>> I don't want to do anything too drastic and take off the patina/color of the rock

Someone may have a better idea, but I can't think of anything that would take off scorch marks other than abrasives. You could try Comet cleanser with something small, like a small wire brush or a flat pebble, and try to clean only the scorched parts.

But those parts will still be scratched up, plus scratches where you overshot. Might as well use something like sandpaper on a fingertip, a Dremel tool or a small grinder wheel on a hand drill.

BUT, after you scrape or grind away the scorches, paint the raw rock surface with a little buttermilk or plain yogurt (or beer?) into which you have ground up some lichens or moss of contrasting or complementary color and texture. That's supposed to be a way to "seed" rocks with interesting lichens or moss.

Moss grows much faster. I speculate that you might get some moss within a month or two by keeping the rocks moist and shaded. Once they're presentable, you could move them to a drier, sunnier spot and see if the lichens take over from the moss. But I read that lichens only spread by 1-5 mm per year! You might try to collect several kinds of lichen so you get at least some compatible varieties.

Grind the lichens or moss finely, or run them with the liquid through a blender (try for a thick slurry, not runny or drippy. One site called the best texture "creamy and spreadable". One site suggested thickening it with corn syrup.

You can paint it on, smear it on, blot it, dip it or finger paint it.

Perhaps the new lichens would grow OVER scorch marks, and eventually hide them without any grinding? Tentatively, from reading, moss likes to have scratches or a rough or porous surface so it can get a grip.

http://vivariumguide.com/grow-...

http://guerrillagardening.org/...

I wonder if you could use a Mr Clean magic eraser?

I agree wit Rick about an abrasive and would also suggest the Scotch green scrubbing pads.They are more flexible and can get into uneven surfaces.

I forgot about the buttermilk trick, may need to do that. That would help out at lot. Thanks!
Will try a scotch brite pad, I keep those on hand.

Scraping with any kind of metal implement might also get a lot off quickly (but leave visible scratches).

You could try Rutland brick and stone cleaner for fireplaces
https://www.google.com/search?...

The Mr Clean eraser would not scratch

Why clean what will be over written by other life?

If you simply must reduce the scorch marks, use buttermilk to re-write the surface with moss-lichen.

A big consideration is what you plan for those rocks.

I personally think leaving the au natural might look
good.

OR if making a type of planter/bed, plant draping
or cascading plants around the edge to cover the
stains. Or soak one stone in a diluted bleach
solution to see how it does .

Bleach is used , along with vinegar in medical
settings.

>>>>Why clean what will be over written by other life?

burnt surfaces are naturally resistant to breakdown and colonization by living organisms. 30+ year old burnt stumps from forest fires are commonly seen here in Minnesota hardly touched by time, where as logged off stumps of the same age have been completely disintegrated long ago.

If you do find something that works, let us know. I have a lovely firepit with a boulder surround. Following some over-exhuberant fires by the younger crowd (bigger is always better I guess...) I'm not too keen on the resultant scorch that runs all the way up the insides and even across the tops of many of the rocks. I expected the bottom inside to blacken, but would like to clean off the tops if possible.

On the other hand, we regularly incorporate burnt logs into our landscape, and mosses and lichens colonize it quickly. This one provides winter interest, and then gets almost totally covered during the growing season with perennials. It also shows more burnt surface during the summer, as some of the mosses dry up in the sun.

I am told the muriatic acid cleans burnt surfaces of rock.

What does "colonize quickly" mean, and how does it compare with non-burnt logs? I would imagine with your warm wet winters of zone 8b Pacific Northwest, the antiseptic chemicals in burnt wood would probably leach very quickly. You are in moss and lichen heaven, no?

Kind of funny story about the burnt logs. My son brought me a burnt log from his nursery as a gift of sorts. I appreciated the gesture and we sited it together and dug it in. I then invited him to go down the hill with me to a rather large burn pile from a previous land clearing project which was off in the weeds a bit. He immediately saw the potential, and told me I was sitting on a gold mine. Since then, he's been dragging random burnt 'yard art' up the hill and placing it in the yard for me. I love the look of it.

Re colonizing, I just let it sit and whatever is already there soon encompasses the logs. Depending on where they are sited, some of the moss/lichen dries up during the summer, then rejuvenates itself over the wet season. I just let it do its own thing. Same with large boulders, some will get green, others not so much. I was unaware the burnt material had any sort of antiseptic nature to it.

Along that line, I also have lots of moss in my gardens and lawn and in some trees. Again, I pretty much just let it be. If it gets over-eager, I'll pull it off newly emerging plants, but I don't get tweaky about it. I like the soft look and assume someone somewhere is likely paying good money for whatever it is I have.

This flat rock serves as a landing for my laundry basket (there is a clothes line running from the deck post up into a hemlock tree directly above the rock) and gets fairly mossy over winter, then pretty much dries up during summer. It has really pretty color to it, different than most rock we find out back.