technical help #1
* home * KILNS * blog * store * pictures * free patterns * technical help * BULLSEYE RODS *
We've been using H and U shaped pieces of metal for over a thousand years now to hold together all manner of coloured and/or painted glass (and you thought we had advanced over the years?). Of course, in our wisdom, we decided to take a metal that's toxic to the human body to do this task. Now that's real bright! In the past 100 years, while we've widened our horizons somewhat by the addition of zinc, brass and copper cames, it is still the uniqueness of lead and its properties that interests us and is the topic of this paper.
MANUFACTURING
Lead today is manufactured by extrusion. This is a rather polite way of explaining a rather painful process that lead is subjected to. It is a process that I am uncomfortable to describe at this time. Just believe manufacturers when they claim that this method is superior to the old days when lead was cast and milled because it allows the molecules of lead "to align in such a way that the lead is stronger. Milling, in which the cames are rolled through a cog-wheel die of successively smaller dimensions is said to elongate the molecular structure, building inherent weaknesses into the came". Let's get Geraldo in on this one.
WORKABILITY
Lead, aside from its cheapness, was chosen originally for its malleability (we pause here while some people rush off to check their dictionaries). The flexible nature of lead is perfectly suited to stained glass. It is easy to manufacture, easy to form and cut and takes solder well with minimal effort. For lead to work, it has to be stretched first (Note: FIG carries only unstretched lead- we believe our customers deserve the enjoyment of stretching their own lead). This straightens the lead channel (came) making the flanges parallel and stiffens the metal and brings boundless enjoyment to those who partake in this activity.
LEAD VERSUS FOIL
Lead offers several advantages over copper foil. Firstly, lead came is more time efficient, thereby allowing the opportunity to pursue alternate and at times more creative leisure activities. It is for this reason that four out of five doctors recommend lead work. Secondly, lead came is structurally sounder for large panels. Because it is soft and elastic, lead is ideal for the combination of compressive and tensile forces to which a window is exposed. Yes, I know, you want this explained to you as if you were seven. Picture wind blowing against a window. Because of leads unique properties it will stretch slightly allowing the window to flex.
LONGEVITY
Lead, unlike marriage to Larry King, is one of the most stable things known to man (except men still won't ask for directions when they're lost). It is very resistant to most forms of corrosion, because it forms a protective patina on its surface when exposed to our lovely and noxious atmosphere (no mother-in-law jokes please) This 'surface rust' gives lead its dull grey appearance and locks in the interior and protects and prevents further deterioration.
Lead is subject to metal fatigue, and often shows up as cracks across the width of the came, usually at the end of a solder joint. Because one of lead's strong points is its elasticity, it is that very quality that can cause it to break down from fatigue. The more elastic the lead is, the more it will stretch. Eventually this stretch ability will be exhausted, and the lead will break. Liken it to bending a coat hanger repeatedly to the point where it breaks. Lead becomes more brittle the more it is stretched. That's why it will eventually break. To prevent this we have to offer proper support and use leads that are not too thin in their profile.
MAKEUP
The composition of lead came has an effect on its longevity. Lead is not made of 100% lead because it would be too soft. Additives such as silver, tin, antimony, tellurium and copper have been added at one time or another throughout the years. It seems today that some very minor amounts of antimony, copper and/or tin (under 1%) is the ideal. These additives stiffen the lead preventing excessive stretching and thereby counteracting brittleness.
If you look at leaded glass panels made in centuries past, you'll see windows that often defy dating, given the incredible stability of the materials used. So while we still can't make an automobile's gas gauge read accurately, we did have the brainpower and foresight to choose lead as the framework material in our chosen craft.
Lead- the Metal
