Imagine the following case:
==> A fire has developed a lot of soot, which now damages a 40 sqm wall painting, which is declared as of "historical importance" ...
Now the soot, mainly from burning shoes, has to be removed, before it does any further damage (which it is said to may, because of attraction of
moisture from the air ... , leading to a sulfatization and thereby destruction of the painting-layer ) ... .
================
The painting itself is of mineral pigments, which last for millions of years in soil, and probably are chemically quite stable to oxidizing
environments ... .
================
Now: Can the soot just be oxidized somehow , at a sufficient rate and at low temperatures ? The layer is thin enough to still let the painting be very
visible, it just darkens it to 50% ... .
I already have tried electrostatically charged brushes of animal-hair, which remove some of the soot, but only half of it ... ... .
Also I have tried a corona-discharge, directly onto the surface, from the 20 kV of an old Monitor ... , with _no_ effect ... ... .
In the literature there are 2 Ways:
==> The mean and plain way of cleaning it with special latex-sponges (not advertising them now) ... , which I havent tried yet ...
==> and newly some athmospheric-pressure plasma-torch , see eg. at http://www.panna-project.eu , but this may be technically too complicated ...
=======
Has anyone any Ideas ? The favourite one would be to oxidize those nano-soot-particles away with some non-acidic gas ... ; ozone wouldn't work, would
it ?
Maybe next I try to reverse the polarity of the corona, since the TV always gives +20 kV, and technologically usually the anode is the workpiece ...
[Edited on 14-9-2014 by chief3]hissingnoise - 14-9-2014 at 06:51
In concentrations necessary to oxidise carbon ozone will likely oxidise the paint-binder and probably irreversibly . . .
Depending on the fragility of the painted surface ─ it sounds like a soap, water and patience(lots) job?
[Ooops! typo edit]
[Edited on 14-9-2014 by hissingnoise]Fantasma4500 - 14-9-2014 at 07:14
this may sound pretty retarded -- but using bubble gum or similar may work to get the soot off, unknowing of how fragile the paint layer behind it is
its hard to tell, idea is that it picks up only more or less loose particles and leaves behind solids that sticks harder to the wallchief3 - 14-9-2014 at 08:39
The bubble-gum idea is similar to using bread, which I tried too ... , some old-timer recommendation ... ; it removes about 50 % of the soot, similar
to the electrostatically charged brush ... ...
There too are some special sponges, called A K A P A D , which achieve better results ... thus far ; I can directly compare it on the wall ... ,
because some official and professional lady has tried it with those, while I was absent ... ; now I search for an alternative ... and maybe a way to
do it better ...
Those said sponges consist of some very soft latex, which is said to crumble upon contact with the surface ... , and to take over the soot just upon
contact , with no frictioning ... ( maybe the surface of those is lipidophilic ... )
The painting-layer itself is quite robust, and massive too ... at least if compared to the soot upon it ... ; it easily reaches the thickness of many
micrometers most of the time, while the soot ist just nanoparticles upon it, with way different reactivity however ... .
The soot typically will be some nano-carbon with maybe some oily ingerdients on it ? subsecret - 14-9-2014 at 08:52
Tell me if this question is too private...
How did the painting get dirty in the first place, and what is it?chief3 - 14-9-2014 at 08:59
Someone laid fire (wasn't catched thus far), and the firemen ventilated the fire through the room with the painting, which is on the ceiling ... . The
painting is some "secco" , the binder was not analyzed so far, a phosphorus-probe could be made to see if its organic ... ; its 140 years old ... .
It's not exactly a michelangelo, but its on the official list of such paintings in the country ... macckone - 14-9-2014 at 10:06
silly putty is used to remove contaminants from delicate archaeological finds
it could be useful for your purpose. Or at least better than bubble gum.Brain&Force - 14-9-2014 at 14:08
What about reducing away the soot? I have no ideas, but it may be a far less destructive approach.Oscilllator - 14-9-2014 at 22:20
I think that given the unreactivity of soot it will be virtually impossible to remove it chemically without also damaging the pigments and/or
underlying canvas. As discussed elsewhere in this forum, carbon particles are immune to just about anything, including hot acids and hot concentrated
sodium hydroxide. Just about the only thing that can dissolve it is a solution of a dichromate in concentrated sulfuric acid. Needless to say, none of
the above substances could be applied to the painting without destroying it.
As such your best bet is probably to remove it in a manner similar to what macckone suggested: with some kind of adhesive. One possible solution that
nobody has suggested yet though is compressed air, although I have no idea how effective it could be.chief3 - 15-9-2014 at 00:40
Compressed air will probably not work better than the electrostatically charged the soft animal-hair-brush ... ; but oxidizing the soot away was my
main idea for question here ...
Also elsewhere I read about ozone affecting carbon-dust ... ; since the soot-particles are nano-sized ... this might be worth a try ...
Thats why I strongly wonder about the fesability of a corona-discharge ... , of some different sort , not what I tried with the positive high voltage
of the old TV ... , which makes the objekt be the cathode ... ; maybe if the object is teh anode it might work better ... , any suggestions for
reading ?
==> The corona might provide some plasma and ozone at the same time ... ...
The pigments and materials used in such paintings are generally stable under oxidizing environments, except maybe for the binder ... ; so a strong
oxidizing environment might do something useful ... , but it cannot be acidic, nor can it be wet ...
For now I'm gonna order some latex sponge, specially made for the purpose, and try it ...
[Edited on 15-9-2014 by chief3]deltaH - 15-9-2014 at 00:41
Here's a link for the step by step removal of fire soot from the Journal of the American Institute for Conservation:
It seems that some "atmospheric pressure plasma jet" is what could do the work ... ... ; searching for a possibility of making one ... ...chief3 - 15-9-2014 at 03:40
If you find a paper you can't access, U2 me and I should be able to get it for you.
Architectural conservation is not my specialty, objects and wooden artifacts are.
I do know that the plasma work is showing promise but have no experience with this.
The sponge/eraser products do work well from what I've seen and they are oleo/lipidophilic. (STAY AWAY FROM ANYTHING CONTAINING SILICONES!!!).
Where in Germany are you, if I may ask. I may know someone near you.
zed - 15-9-2014 at 12:28
Try not to rub the soot into the surface of the painting. One idea, if possible, would be to put an electrostatic charge on the painting. That would
cause the painting to repel the soot, since they would both assume the same charge.
Also, silly putty sounds like an excellent idea. If it is a possibility, simply press a thin sheet of it directly on a test area. No rubbing!
When you peel it off, there is a good chance it will take the soot with it. Worth researching!
Vacuuming.morganism - 15-9-2014 at 15:04
recipie for silly putty on "how to geek", and many cooking sites.
I understand nitric oxide is a precursor to hydroxyls, perhaps some exhaust is in order.....
there is also some studies on removing hydrocarbon soot from churches with bad ventilation, and lots of candles that may be of use....
barbs09 - 16-9-2014 at 06:21
Application of Sticky tape with careful peeling? Or the stuff that protects LCD screens?argyrium - 16-9-2014 at 13:58
You might also wish to look into "dry ice" cleaning.
Google "soot removal" and "dry ice" and you will find lots.
Here is one trial use.
Attachment: apnewsvol15no3.pdf (342kB) This file has been downloaded 491 times
The use of 'sticky' materials would be difficult to control. The use of aqueous and solvent borne poultices have been done on masonry with various
degrees of success. Sometimes the absorbent material of the poultice can become lodged down in the surface morphology of a rough finish and is
difficult to clear.
The use of 'silly putty' type of materials would have to be carefully considered and tested. Many of these materials contain plasticizers and/or
other non volatile compounds that may be absorbed into the surface of the object being cleaned. Little_Ghost_again - 18-9-2014 at 02:03
Really old and valuable tapestries are cleaned with the extract from the soap wort plant. It is apparently the first type of soap ever used and is the
mildest detergent known to man.
Its slow but exceptional at cleaning in a very mild manner, its used a great deal in restoration work including the first step in cleaning works of
art over 500 years old.Zyklon-A - 18-9-2014 at 05:26
Do you know what the paint is? Like you said in the OP post, paints tend to be very inert, likely oxidized to their highest (or only) oxidation state.
If it's white, it is probably titanium dioxide[REF], which is resistant to nearly all acids - especially those that are strong oxidizers, as it is in it's highest oxidation state
(+4)[REF].
Or are you more afraid of physically destroying the pigment by roughly using too strong abrasives or whatnot? In which case, I don't really have
answers...zed - 19-9-2014 at 15:15
Pressing a mildly adhesive tape onto the surface (if it is fairly flat), is also an possible option.
Either Blue painters tape or drafting tape, might work well. Watch out for regular masking tape; it is too sticky. Under some conditions, paint may
adhere more strongly to the tape, than it adheres to its undercoating. It is important that your paint remains where it was intended to be. On the
ceiling.
Once again, watch out for residue. And, this will cost some money. painter's tape is kind of spendy. AJKOER - 23-9-2014 at 17:36
Apply some steam and then sprinkle/spray/gently brush on nano-sized magnetic sensitive iron particles (from heating iron oxalate, or the acetate...).
Then magnetically remove the soot and iron (no references, original idea may or may not be effective).
Advantages: not physically abrasive, not chemically destructive.
Disadvantages: Must be thoroughly removed after application to avoid chemical alteration of the Iron oxide that could contribute to staining. AJKOER - 25-9-2014 at 10:08
If there exists an oil (perhaps olive oil) that is actually benefical to the surface of the painting, just gently apply in excess and remove with a
soft absorbent cloth.
Hopefully some of the soot is washed off in this benefical oil 'bath'.chief3 - 28-9-2014 at 07:54
Well, thanks that far, I tried until now the following:
==> kneadable eraser : Successful as the conservators result, but slow (maybe 1 sqm / day) ... and leaves some small white dots, where it takes the
painting-layer away completely ...
==> self-made 10 kV-arc-plasma, at maybe 2 mA ... ; this actually _works_ in principle, but slowly since only a very small area can be treated at
once ... ; I tried it not on the painting, but on a porcelain-pistill, which I coatet with soot from a candle ... .
The voltage-source is a flyback-transformer, connected to 3 V at 25 kHz, which gives something in the range of 7 or 8 kV , at max. 3 A on the primary
side ... which gives an Idea about the wattage (5 - 10 Watt) and the max. HV-current (1-2 mA, maybe more at a voltage-drop during arcing) ... .
A plain corona doesn't work, neither positive nor negative ... ; also plain spark-discharge does nothing ; it has to be the sort of continuous arc
that has some red-violet gas-zone ... , which is a plasma ... .
==> This then, when close enough to the surface (nearly directly on it), _does_ remove the soot ... ... .
=======
Now I wonder about ho to expand that plasma-zone, and how to bring it better onto the surface to be treated ... ; ... ; basically I think of some sort
of an plasma-burner ... ... ; wonder if a Tesla-discharge might work ... ; (as I said plain arcs don't work, this probably also counts for plain
tesla-arcs) ... ... .
==> Maybe I just have to blow air through a discharge of some sort ? ??
Now I also will order some of the pads used by the commercial conservators, to see ... if these just might do it ... .
=======
Now:
@morganizm ... : What is it with the bad venting ? ?? Maybe some CO2 does combine with the soot ... to make CO ... , somewhere in the possible
equilibria ... ? CO2 and CO maybe reactable with soot ... , since these are chemically related ... ... ; everyone knows that a coal-fire is best
started by already-burning coal ...
@argyrium: The dry-ice method is said to be too abrasive (conservator), and would potentially destroy more than it may preserve ....
@Zyklon-A: The paint is some sort of secco ; its on the wall, but it's not an oil-painting ... ; it's just pigments with some sort of binder, and the
binder wasn't determined so far ... ; it's from the 1800s ... , and therefore will not contain any TiO2, but other pigments which are certainly nearly
as stable ...
@little_ghost_again: Wet cleaning is not possible, it would flood the pignemts around, and destruct the painting ...
@morganism: The nitric-oxide sounds very interesting ... ; where can I read on ... ? I have some sulfuric acid (concentrated), quite much nitric acid
(53%), and some nitrated, eg. of Barium and Sodium ... ...
Hopefully its not acidic, since the pigments may be of the carbonate-sort ... ; at least aome of the painting will contain carbonates, and if its only
the chalky layer below the paint ...
Thanks that far, now I'm gonna study all of your links ... ...
[Edited on 28-9-2014 by chief3]Oxirane - 29-9-2014 at 01:46
Vacuum it? chief3 - 30-9-2014 at 00:59
vacuuming not possible, doesn't work ... : Soot adheres to well to the surface ... ; but some parts of the painting would be destroyed by the suction,
because they are too loose ... ...
[Edited on 30-9-2014 by chief3]Dan Vizine - 8-10-2014 at 10:22
This may sound a bit off-the-wall, but the melamine pads they sell in supermarkets are very efficient at removing carbon gently.
They are called "Magic Erasers" (or something like that).
If you buy the Chinese versions on eBay, they are very flimsy. Maybe that's a good thing in this case?
