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JP2
AGG member
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Fri Nov 17th, 2006 11:05 pm |
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Ran into a problem we've not seen before on some windows. Perhaps the right coasties may have seen this....Went to a job in the San Fransisco Bay area and found a reddish oxide deposit on the outside of four windows. Of these windows,two were made in 1957,one was made in 1967 and one was made in 1978. The latest one was made locally to the area,the others in Europe.
The deposits were hard and scraping them off showed the lead underneath to be sound,without pitting or crumbling. These windows are on the weather side of the building,about 4 miles from the bay; the rest of the lead was bleached from exposure but overall in good shape. The 'oxide(for want of a better word) seemed to be mostly around the joints but flowed on the lead too....Overall,it made the windows look 'rusty'. A re-putty and good scrubbing darkened the windows again,the client wishes outside covers installed at a later time.
Anybody have any ideas what this was? Windows were in good shape,had to pull a couple to flatten out bows and they were still tight overall...hmmmmm...JP2
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Vic
Director
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Posted: Fri Nov 17th, 2006 11:28 pm |
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| Was this red stuff inside and outside? Sounds like they may have used rosin for flux. It's red/brown in color and hard.
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Krueger
Director
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Sat Nov 18th, 2006 12:09 am |
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| Does the sprinkler system land on those windows when it is on? May just be rust deposits out of the water/sprinkler.
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gwsg
AGG member
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Posted: Sat Nov 18th, 2006 05:17 am |
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G’day Jim,
I’m not a right coastie, I’m a bottom coastie but I have seen this situation before. I have attached a photo, which I hope will come up, that I believe is the situation that you are describing.
Lead oxidises in different ways identifiable by colour. White oxide, brown oxide, red oxide, black oxide depending on the corrosive agents or atmosphere it is in contact with. What you describe I take to be brown oxide as in the photo. Brown oxide and black oxide actually form a protective layer over the lead preventing further corrosion as opposed to white oxide and red oxide that eat away at the lead gradually consuming it.
The lead in the photo is situated less than a mile from the sea and is quite exposed however, I have also seen brown oxide hundreds of miles inland so it is not the salty atmosphere alone that will cause this. More likely the materials and manner of installation creating a particular acid that will have this effect.
As you discovered, when the brown oxide is scraped off, the lead underneath is in good condition as opposed to the areas of white oxide which leave the lead pitted and dry. When we re-cement a window, the fatty acids that make up linseed oil will cause the protective black oxide to reform on the surface of the lead offering protection for the future. Hovever if the corrosive conditions continue to exist, the white and brown oxide will return. I think protective glazing will only compound this.
cheers
GeoffAttached Image (viewed 231 times):
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Roberto
AGG member
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Sat Nov 18th, 2006 03:11 pm |
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Good morning Jim,
I have seen this type of oxidation myself in windows in the northeast, in particularly the Boston area where I live and work. I am not certain why and what causes this brown oxidation but I agree with Geoff in that I don't think the vicinity to the water is significant, as I have seen it on windows that are near and far from the ocean. Maybe someone in the group has actually had this tested.
Good luck,
RobertoLast edited on Sat Nov 18th, 2006 03:15 pm by Roberto
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JP2
AGG member
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Posted: Mon Nov 20th, 2006 12:29 am |
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| Bingo!! Our antipodian member hits it on the nose! His pics show exactly what we found...We'd thought it could have been a flux reaction but showing on all the windows of these different ages and makes? They're not hit by sprinklers or we would have thought water deposits,too. We thought it could have been a spray mask applied over the windows by a paint crew and not cleaned off or jet fuel,they are under the SF airport flight path....Thanks for the replys,folks, we can tell the cilents not to worry to much,dookie(as they say) happens. JP2
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PatrickClark
AGG member
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Thu Dec 28th, 2006 11:50 pm |
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Greetings,
After 25 years of restoring leaded panels I've never seen red oxidation like in the pic. I'm right on the ocean coast and work inland as well. Most windows here, even from before turn of the century, are covered with protective glazing...
When cleaning in the cementing process you described, does the color disolve like a sodium based oxidation or does it flake off like a surface coating...i.e. paint? Is it possible that at some point in stained glass history it was popular for some glaziers to coat the lead surface with a thin red oxide based primer paint to preserve the lead? The pic shows equal oxidation on both lead and solder surface... would the same oxidation occure so evenly on two different surfaces like that?
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artfem
Administrator
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Posted: Tue Jan 2nd, 2007 10:28 pm |
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There are a number of oxides of lead that are compounds with varying numbers of oxygen atoms per molecule, depending on the valence state of the lead (+2 or +4) with which the oxygen reacts. “Valence state” can be understood as a measure of how many covalent bonds (the sharing of electrons by two atoms) will be formed when the two element or compounds react with one another. The chemical and physical properties of the different lead oxides are a function of how many oxygen atoms bond within a molecule and the shape of the crystal that is formed. How the molecule forms can be affected by the chemical composition of the lead alloy (even “pure lead” typically has some impurities); temperature at which the molecule forms; micro-environment at formation (enclosed space, moisture levels, presence of other chemicals, etc.).
Lead monoxide, used extensively in the production of lead acid batteries, is a dark grey in color. Minium, commonly known as “red lead” can range in color from scarlet to brick red. Lead dioxide (also known as lead peroxide) is brown in color, insoluble in water and is a known carcinogen. It is my guess that the reds and browns that are being reported on certain lead cames are one of the above oxides. These oxides form on the surface of the lead cames and should have little or no adverse affect on the structural integrity of the lead. They are all highly toxic and as mentioned above may be carcinogenic so they should be treated with extreme care.
Lead carbonate replaces the lead and forms an open, powdery deposit that allows for the continued attack of the lead below. The chemical process is as follows: Acetic and some other acids, in the presence of carbon dioxide, catalyze with lead to produce lead acetate and lead hydroxide. Lead acetate and lead hydroxide together react with carbon dioxide and form lead carbonate. Lead carbonate then releases acetic acid and the process can become self-sustaining. It is important to recognize that the formed lead carbonate is not just a substance clinging to the surface the lead, it is the surface of the lead transformed to powder. For practical purposes, a portion of the lead is gone and lead carbonate is left in its place. This product of corrosion is indicative of a more harmful type of corrosion and if the micro environment that encourages this corrosion is not altered, the lead matrix will ultimately fail.
Art Femenella, Director
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PatrickClark
AGG member
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Tue Jan 2nd, 2007 11:55 pm |
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Hi Art,
Have you seen that color of oxidation on many leaded windows here on the East Coast? Do you think oxidation like that would form as a similar color on both the lead and solder joints. It also looks similar to the color of a beautiful, rich red patina that occasionally forms on bronze. Did lead makers ever use bronze or a bronze by-products as an alloy in lead?
That red surface in the pic appeared to kind of flake off and the lead surface left exposed under it looked intact- not pitted or degraded. Would an oxidation that formed and was then removed... with the oxidation actually being... I think you said, a result of the lead breaking down... could it be so thin that the remaining lead would still look so good... or if the lead surface degraded would the remaining lead appear more grainy and degraded like when you remove an apparent white, crystalline, sulfide looking oxidation?
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Tod
AGG member
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Posted: Wed Jan 3rd, 2007 03:17 pm |
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I, too, have seen the stuff in Geoff's pic, working mostly on windows here in central and western Massachusetts. I thought it was a treatment rather than oxidation because it does seem "flakey" (although fairly well-bonded), the lead beneath is in good shape, it's on both the leads and solder joints and the color is so even.
My 2¢ worth - Tod
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artfem
Administrator
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Wed Jan 3rd, 2007 04:56 pm |
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One of the primary uses of the lead oxides is as pigments. This is probably why they appear to be an applied "paint". The oxides form in a very fine crystaline structure and remove only a surface layer of the lead from the came. I agree that you do not see the pitting or obvious, physical signs of corrosion you see when lead carbonate is formed. This is partially due to the fact that you are inspecting with the naked eye. Under even modest magnification, you will see pitting of the surface.
Bronze is an alloy made from copper with tin as the prime additive and other trace elements to achieve specific properties in the alloy. I have never heard of bronze being added to lead cames, and doubt that trace amounts would result in the depth of color seen in the red coating on the lead in question. Trace bits of copper do exist in the ore that lead is refined from. In modern leads, trace amounts of copper (much less than 1%) are added to benefit the formation of homogenous crystals as the lead moves from a molten to solid state. This offers a benefit in resistance to metal fatigue failure.
I am by no means certifying that what has been reported are oxides of lead. In my opinion, this is the most logical conclusion. The next step would be to do some testing. If it is an applied "paint" it should dissolve in some solvent. If it does dissolve in a solvent, it would be easy to then see if any of the lead oxides dissolve in that same solvent. The most definitive test would be to send a sample out for chemical analysis.
I have seen painted cames before. The painting is typically done after the panel has been completed and waterproofed. Typically, the paint is also present on the glass, and there are spots on the lead that have been missed during the painting. I have seen leads that have been gold leafed as well.
Art Femenella, Director
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mmezalick
AGG member
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Posted: Thu Jan 4th, 2007 08:40 am |
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What would be the correct measures to take in this situation?
Remove the oxidation or not? And of course, by what means would be the most recommended? Wire brush or would that be too harsh?
So many questions . so little time.
Michael
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Ardbeg
AGG member
| Joined: | Tue Oct 24th, 2006 |
| Location: | United Kingdom |
| Posts: | 67 |
| Status: |
Offline
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Thu Jan 4th, 2007 10:52 am |
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The question is not "should one remove the oxidation or not", but rather: "What has caused this effect?" and "How can I prevent it from re-occurring?"
Simply removing any surface deposit, but not controlling the problem / environmental conditions, will simply encourage more degradation to take place, and, once the surface has been eroded, possibly the erosion will take place quicker.
First, get an accurate analysis of the deposit - don't hazard a guess. If you don't have pigment analysis equipment in your studio, then take a sample to somewhere that does, if you consider the deposit important enough to lay out the expense. Paint conservation studios / wall paintings studios, and museums should have this equipment / training.
Second, find out why it has occurred.
Third, try to prevent further occurance.
All the best for 2007 everyone,
Linda
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mmezalick
AGG member
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Posted: Thu Jan 4th, 2007 11:51 am |
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Lindia,
I aggree with your three suggested steps but the question does still remain.
What should be done to the existing oxidation and what are the best or recommended methods if removal is the correct or recommended action?
Michael
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Ardbeg
AGG member
| Joined: | Tue Oct 24th, 2006 |
| Location: | United Kingdom |
| Posts: | 67 |
| Status: |
Offline
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Thu Jan 4th, 2007 12:54 pm |
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Personally, I wouldn't scrub at it with a wire brush. If it shifts with a soft bristle brush then take care when brushing, as the lead deposits are easily inhaled, make sure all H&S precautions are taken. If it doesn't come off with a soft brush, then is it really a problem? If it's a paint, then, as Art said, a little solvent would remove it, like a turps / linseed oil mix - that shouldn't do anything any harm and it would disolve the overpainting on the lead, if, indeed that's what it is. The only proviso would be if there is glass paint nearby - that, of course, changes everything, and what you do to the lead has to be reconsidered.
Therein lies our dilema as we work with lead, glass and pigments: Chemical solutions such as EDTA which can be useful in "cleaning" lead and removing lead compounds, can be extremely harmful to glass; and paint strippers, such as methelene chloride, which clean old oil based paints can also overclean glass paints if they are not in perfect condition.
It's really a balancing act - what is the most important surface to clean / save? Invariably it is the painted glass surface. The lead structure, if it's strong, albeit unsightly, comes down the priority list to be cleaned if, by cleaning it, you compromise the structure of the lead.
Again, it comes down to the question - why does the lead look like this? and try to prevent any further deterioration. If it's just paint, then the environment is safe. If it's a lead compound, then find out why such a corrosion product has occurred and deal effectively with the cause - preventive conservation is often more effective than physical treatments which potentially can cause further damage.
Linda
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artfem
Administrator
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Posted: Thu Jan 4th, 2007 09:35 pm |
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Linda: Great to hear from you! Thank you for entering the forum. Of all the irony, I was in NYC today and happened upon a place in midtown that advertised itself as the only Scottish restaurant in NYC. And I thought McDonalds’ had been there for years....
I tried to be clear in my posting that I was offering a best guess as to what the deposit is and I fully agree that real testing should be done to verify what the material is. Next step should be to determine if the compound will harm the lead or the glass. Next step to try and determine what is causing the deposit to form and to then mitigate or eradicate same. I would also agree with you that if it doesn't come off easily, why take it off at all? Unless it is harming the lead or glass. Also agree that wire brushes should not be used. Firstly, due to risk of scratching glass or paint; and secondly, wire brushes may remove some of the corrosion, but tend to force a bit of it down into the soft lead came. I would rather start with a soft brush and then move to a hard wood pick or careful use of a metal tool to scrape the corrosion off of the lead. Finally, as I mentioned, all of these compounds with lead are very poisonous and some are carcinogenic. Extreme care should be employed when removing them.
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gwsg
AGG member
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Sat Jan 6th, 2007 06:16 am |
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Michael said:
“I agree with your three suggested steps but the question does still remain.
What should be done to the existing oxidation and what are the best or recommended methods if removal is the correct or recommended action?”
Michael, I will describe the actions that we took in the case of the window in the photo.
Firstly, I would automatically expect everybody to take appropriate precautions suggested by Art and Linda regarding evaluation of the problem and possible damage to window, building or personal health.
The brown oxide in the photo I believe to be lead dioxide. The white oxide I believe to be either lead sulphate or lead hydroxide rather than lead carbonate which is far more aggressive and reactionary. Of the 2 oxides the brown is benign and the white is malign as explained earlier, so really the brown is of little concern it is the white oxide that is corrosive. The window had been subject to unvented double glazing for about 30 years which is the situation where aggressive oxidation is most likely to occur.
I am surprised that so many of you seem to be unfamiliar with this situation and it may have something to do with climate. I live on the driest continent and although we can usually expect good winter rains, in summer the land totally dries out due to extreme heat and very low humidity. Plants have adapted to die back in summer and regrow in winter or spring and this is what also happens in the micro climate inside the double glazing space.
Visit the window in late winter and there will be moss, algae and/ or lichen growing in the glazing cavity, visit it in late summer and there will be no green plant matter at all, just the dry, powdered remnants of last years growth. My belief as to the cause of brown oxide, in this case, is that when the rains come again and water leaks into the glazing space, the powdered plant matter is dissolved to form organic acids which, when the glazing space heats up, vaporise and then condense on the surface of the lead with which they react to form brown oxide. Monitoring has shown that removal of the exterior glazing prevents reoccurrence.
As to removal of the white oxide, we firstly clean the window and lead with stiff natural bristle brushes and then carefully remove the white oxide with wire brushes. In the hands of an observant and experienced operator there will be no damage to glass or paint using this method. No excess force is required as the particles of white oxide fall off quite readily often without disturbing remnant areas of black oxide. We usually take off the brown oxide also but more from a matter of aesthetics rather than need.
During the recementing process, the fatty acids that make up linseed oil will react with the clean lead surface to reform a covering of benign black oxide as for a new window. Much the same process as descaling rusted ferramenta before treating with a rust converter.
cheers
GeoffAttached Image (viewed 136 times):
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gwsg
AGG member
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Posted: Sat Jan 6th, 2007 06:18 am |
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| Wire brush Attached Image (viewed 134 times):
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gwsg
AGG member
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Sat Jan 6th, 2007 06:19 am |
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| White oxide removed Attached Image (viewed 134 times):
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gwsg
AGG member
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Posted: Sat Jan 6th, 2007 06:20 am |
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| Black oxide reestablished Attached Image (viewed 131 times):
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