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vohara
AGG member
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Fri Feb 29th, 2008 04:33 pm |
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| I suggest to my customers to allow the lead in their new stained glass windows to age with time over the use of patina because I recall reading that the natural process is prefered. Is there any technical information on why natural aging is more appropriate than using patina?
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glasman
Director
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Posted: Fri Feb 29th, 2008 08:00 pm |
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Patina is an acid. When it is used on a leaded panel, it gets under the flange of the lead and there it sits, eating away at the came.
John Raynal
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Mary Clerkin Higgins
Director
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Fri Feb 29th, 2008 11:34 pm |
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| Elbow grease and a soft shoe-brush will darken the leads without needing patina. Mary
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Olimpia
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Posted: Fri Mar 7th, 2008 11:28 pm |
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I haven't done many pieces that are not either installed or framed in wood. I have a few in the process now that will be framed in zinc. My customer wants the zinc to match the natural dark lead that putty and elbow grease is seen through out the panel.
I don't really like how anything looks, I'll have to settle for a dark but not even look patina gives to zinc, since painting the frame is too stark of a contrast and looks artificial.
I suppose I am wondering about the contact that the patina has on the lead that touches the zinc border. Is there a way to neutralize the acid? Would applying more whiting and more brushing once the zinc border is patinaed be enough to neutralize it.
I just don't like patina!
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Roberto
AGG member
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Sat Mar 8th, 2008 04:15 am |
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You should not solder lead to zinc. By doing so you will create a battery.
Plus, I really don't see the reason in using zinc on the perimeter. There is a myth that using zinc on the perimeter will make the stained glass panel stronger. I have recently removed 90 year old English windows from a church where the surrounding stone needed some serious work. The windows must have been a bit too big originally for the opening as there was no lead around the perimeter, just glass into the stone and yet there was no sign of fatigue or deflection. I have seen this many times. The material used around the perimeter, in my opinion, does not add strength to the stained glass panel, and you should definitely never mix lead and zinc.
Good luck,
Roberto
Serpentino Stained Glass
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David Crane
AGG member
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Posted: Sat Mar 8th, 2008 04:43 am |
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Roberto,
Aside the patina problem, you have hit on an aspect which has often perplexed me- Can't tell you the number of window sections I have excavated which have had no border leads - obviously trimmed by the setters on site. Is it possible the communication between the size takers and the layout people was so poor? And why are they always oversize? Very rarely do I find extra leads at borders to fill up space or as my old Maestro (sorry Charlie) used to say " your tool box has half inch putties, three quarter inch putties, one inch putties, what ever you need, to fill the space left over from those incompetant SOBs who took the sizes....."
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mmezalick
AGG member
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Sat Mar 8th, 2008 10:00 am |
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Roberto.
I have also seen many panels that have a zinc border without any problems and I do understand the "battery" effect, but I don't think it is that much of a problem as it sounds. You could not run a light bulb of the connection so why worry. As for my teacher, I was told , jokingly, that the border lead was only good for moving the panel from the bench to the opening. Once set, the window really did not need the lead, as we have all seen with the panels described. Now, I am not advising anyone not to use a border lead just helping to share what I have been told. One solution for Olimpia is to tin the zinc and them buff it when she is finishing the panel. It will look like the solder joints.
Michael
PS I prefer an all lead panel, just in case the panle size is too big, It's not easy to shave down zinc.
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Olimpia
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Posted: Sat Mar 8th, 2008 02:49 pm |
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Hello,
Maybe I wasn't very clear, these panels that have the zinc border are only small hanging on chains decorative pieces. I never use zinc on the border of panels to be installed either in an architectural setting or in a wooden frame.
I don't think there is anything to gain by it and much to lose (if trimming is needed). Although if you are shipping these smaller panels that will be installed by a customer, if they are on the larger size I might add zinc, just because they don't know how to handle them.
These are not panels that will be historically important in any near future mind you, yes, hate to admit it but they are probably landfill pieces. My hanging pieces commissioned by customers. I can't see their great grand-children's generation still thinking they are so great.
But I do have a few that they will, or so I want to believe!
Tinning seems like a good idea though!
Last edited on Sat Mar 8th, 2008 02:52 pm by Olimpia
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Roberto
AGG member
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Sat Mar 8th, 2008 06:17 pm |
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Michael,
I have seen countless examples of lead soldered to zinc, where after only a few years there is significant corrosion. My question is simply: If you can achieve the same results with lead, why use zinc? And I agree with your teacher's statement by the way.
David, I have always been amazed at how often I find the nicest of windows, many by important artists, where there was obviously a disconnect in communication from when the size was determined to when the window was fabricated. Someone wasn't careful.
While on the subject of sizes and perimeter lead: I have removed and worked on many windows by the Tiffany studios. I would say that most of them if not all, had the perimeter leads tinned (floated with solder). After over 100 years, there is virtually no corrosion and the original lead was left in place whenever possible. But interesting to note that the perimeter lead has never been shaved down or removed to fit the opening. The guy taking is sizes must have been very good.
While working on a La Farge window recently, the exterior surface of the leads were floated with solder, with the exception of a small 8" strip. An oversight by the glazier (I assume). While the floated leads showed some corrosion, the 8" strip that had not been floated had disintegrated.
I'd like to hear others' opinions on floating perimeter lead or floating lead in general. If it prolongs the life of the lead, should those fabricating new windows today adopt this technique?
Happy weekend everyone!
Roberto
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mmezalick
AGG member
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Posted: Sat Mar 8th, 2008 06:31 pm |
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Roberto,
I have also seen the floating of solder on the perimeter lead including the Tiffany I am working on now, except it is only floated on the "front" side.
It was made in 1897.
Also I have found that the outside flanges of the perimeter lead, in several cases, are cut close to the heart.
They have also floated the solder on many, if not all, of the layered areas where one layer is made up of several pieces and the next is a single piece of glass. The multiple pieced section is the one that is floated but only on the side that will be covered.
Other then for a free hanging panel, which I rarely do, I would never use zinc as the perimeter as I find it just one more thing to deal with, when it is not needed.
As for floating new work, maybe that's why some lead companies are making the leads harder.
Just a thought.
Michael
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Kal Tiki
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Sun Mar 9th, 2008 06:09 pm |
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| Hi Guys, I have been tinning my perimeter leads for about 10 years. I noticed the same thing with perimeter leads. Some leads were like paper from the ravages of water, organic acids, etc yet the solder joints were bright and like new. It made sense to float the leads with tin. And for my new work I always float all the leads, like LaFarge and Tiffany, because I think it does add strength. But I will also do some kind of patina on the tinned lead, either black, copper, or hot copper. I noticed that a tinned window doesn't create the nice dark brushed patina from waterproofing that an untinned window does. But on the flip side of the coin I can control the chemical patina on tinned leads so I do that then waterproof. Dan Maher
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Mary Clerkin Higgins
Director
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Posted: Mon Mar 10th, 2008 12:04 am |
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On all of my new pieces, except large-scale architectural ones, I tin all the leads to avoid the visual jump from soldered to unsoldered areas. Then I darken them using a soft shoe-brush, after puttying. Years ago while in England, I got some tubes of black paste used to darken cast-iron stoves that glaziers were using to darken the leads as the last step. I'll bet it was fine for the leads, but it left a residue on the glass that then required another cleaning. The shoe-brush alone does the trick very well. Mary
Last edited on Mon Mar 10th, 2008 03:16 am by Mary Clerkin Higgins
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bbates
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Mon Mar 10th, 2008 01:15 pm |
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About a battery...
I don't know why creating a battery would be a bad thing, the amount of juice created (if any at all) would be so small it would be insignificant. What do you do with foil panels? You are mixing copper foil (one metal) with solder (another alloy)? Not to mention the frame, I have repaired so many hanging foil panels with lead borders that have fallen within a few years because the lead stretches...
I have a few scientisit friends, I'll run this by them and see if they have any good information. When we use zinc for a border it is because it's hanging, the border is going to be exposed, or it very large and we need the extra strength.
We use lead when we question of accuracy of the opening, or they are smaller...
Not that big of a deal, I hope I'm not going to get hate mail for this... LOL
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Mary Clerkin Higgins
Director
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Posted: Mon Mar 10th, 2008 05:01 pm |
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Zinc in situ, whether in contact with lead or not, is more susceptible to corrosion than lead. I’m posting a photo of a zinc-came window that has a round lead flange in the bottom-right corner. The photo shows the side that was exposed to the weather. The flanges of the zinc came are full of holes, separated and drooping. In this case, the battery effect has not caused any problems with the lead/zinc connection, but the zinc, used for strength so no bars were needed, has deteriorated badly. The side not exposed to the weather did not have any pitting or separation. The window (eleven stories up in an apartment building) was holding together, but seriously weakened. I’m also posting, a photo showing how the sun had shifted the color where the glass was exposed, from clear to purple due to the manganese in the glass. You can see that the edges and where the glass had been covered by a round lead flange are still clear.
The problem with zinc in an architectural setting is that, while more rigid than lead, it is more susceptible to corrosion, so, long term, it has properties that can make it weaker than lead. As has been mentioned on this thread, once a panel is in its frame it doesn’t need a rigid border - panels with no metal border at all survive just fine. So using border zinc architecturally, just for ease of handling, is building in a problem. However, using zinc for small panels that will not be up against the weather (since moisture seems to significantly exacerbate the problem) is not a significant problem, but I’d say only small panels, larger, free-hanging panels I would want to put in a wooden frame, for a variety of reasons. Mary
Attached Image (viewed 59 times):
 Last edited on Mon Mar 10th, 2008 05:03 pm by Mary Clerkin Higgins
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Mary Clerkin Higgins
Director
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Mon Mar 10th, 2008 05:02 pm |
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Here's the photo showing how the sun had shifted the color where the glass was exposed, from clear to purple due to the manganese in the glass. You can see that the edges and where the glass had been covered by a round lead flange are still clear.
Attached Image (viewed 57 times):
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artfem
Administrator
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Posted: Tue Mar 11th, 2008 05:08 pm |
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It is not the amount of current flow (amperage) that is the problem; the problem is that any flow at all corrdes the zinc. Galvanic corrosion is the problem. When dissimliar metals are placed in contact and in the presence of an electrolyte (a liquid, typically an acid - ph from 1 to <7-) such as the acid in your car battery. For galvanic corrsoion to occur, all of these conditions must be present. That is why using a zinc perimeter for a gallery piece is absolutely fine.
The simple fact that two dissimiliar metals are joined and an electrolyte is present does not always result in galvanic corrosion. The two metals must be far enough apart on the "galvanic series" to develop a sufficient "electric potential" (voltage) to begin the flow of metallic ions (in this case negetively charged parrticles) to flow from the less noble (more active) metal to the more noble (less active) metal. The result is the corrosion of the less noble metal, in this case, zinc. This is why zinc collars are placed onto the propeller shafts of boats; the zinc corrodes away protecting the metal of the propeller shaft and nut from corroding.
The stronger the electrolyte, the quicker the corrosuion. This is why lead/zinc panels in marine environments corrode faster. I have seen hundreds of panels made between 1915 and 1940 that combine zinc and lead cames in the San Francsico area. Virtually every interface or solder joint between the two metals evinced corrosion. M<nay to the point where the solder joint had completely failed.
While the analogy provided is to a battery, the actual shock experienced is not electrochemical in nature; it is financial and comes from the failure of the panel.
Art Femenella
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artfem
Administrator
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Tue Mar 11th, 2008 05:34 pm |
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This a common occurence and is referred to as solarization. Some glasses that use arsenic as a decolorizer can also be subject to solarization, but the glass turns brown. Decolorizers were added to less expensive glass to make them clear. In the original batch (dry mix of compounds that are placed into the furnace), there are often impurities such as iron that can imbue a color (green) in the finished glass when clear glass is desired. Decolorizing agents such as manganes and arsenic are added to the batch to cancel out the unwanted color shift.
Sometimes these decolorizing agents are not stable or too much is added to the batch. Due to ultraviolet radiation exposure from the sun, the decolorizer becomes active and over compensates for the original color resulting in turning the glass purple (such as most of the glass in doorways in the Back Bay section of Boston) or dark browen when arsenic was present. This process can be reversed in most cases by heating the glass to 500 degrees centigrade. However, this approach is not advisable for conservation projects. As Mary notes, the part of the glass that is shaded from the ultraviolet remains the original color.
Art Femenella
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artfem
Administrator
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Posted: Tue Mar 11th, 2008 05:36 pm |
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Another problem with zinc is that it is a folded metal and thereby hollow inside. The zinc corrodes both from the the outside in and the inside out. Very difficult to properly clean and resolder as well.
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joseph2bears
AGG member
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Tue Mar 11th, 2008 05:39 pm |
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The battery that is formed by a lead to zinc interface is a very weak battery. When water is present, particularly with airborn contaminates, the water will ionize. These ions will strip electrons from the zinc and transport them to the lead. The battery voltage produced by this action is very small and the electron flow is miniscule. The power produced is useful for only one purpose: galvanic corrosion! This is why the zinc slowly corrodes away. It is the reason zinc borders are not recommended.
A battery is formed with two metals, one with an extra electron is its outer shell, and one missing an electron in its outer shell, in the presence of an ionic transport vehicle, either acidic or alkaline. Some combinations can produce useful power, but most just produce galvanic corrosion.
And what few realize in this day and age is that the power equation for any useful battery is a net power loss. That is, it takes more net power to manufacture a battery than the battery will ever return. The metals have to be mined, refined and formed, and the chemicals have to be produced. There's a message for all the greenies with their cell phones and iPods!
--Joseph 2bears
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bbates
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Posted: Thu Mar 13th, 2008 11:37 am |
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still beating a dead horse... pardon the expression to you horse lovers...
We have removed many old window 60+ years old with zinc borders and the metal was not horribly corroded. I have a few questions...
A. Could the environment have something to do with the corrosion, midwest vs. coastal areas? Perhaps the air has more corrosive elements on the coasts.
B. We almost never put in windows without stormglazing or insulated units in front of them to prtect from the elements. Does this "corrosion problem" still applu to these windows not directly exposed to outside air?
C. We feel some windows NEED the extra rigidity for transporting and install. Would H zinc be any better than U zinc? The U is one layer hollow and the H is double layered folded all the way through, so...
I've not come across windows as corroded as the pic in one of the previous responses, that is why I wonder if the environment can play a major factor; pollution, natural acidity of the air, chemical used in the surrounding environs, etc...
I'm a jus' tryin' ta get edukated heree...
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