Came: Straighten vs stretch

In dealing with lead came there is often reference to “stretching the lead”.  This frequently leads to emphasis on making the lead came longer. However, this is a misinterpretation of the phrase.

The object in pulling on the lead is to straighten it.  No more effort needs to be put into the lead once it is straight.  In fact, further stretching can lead to weakness.

The upper strectched came has an orange peel texture and the lower straightened does not

You will see an “orange peel” texture on the surface of the came when it has been stretched beyond its tensile strength.  This indicates considerable weakness in the metal.

The upper piece illustrates the visual effect of over stretching leading to the weakening of the came

A test to show relative strengths in stretched and straightened came uses two short pieces of came from the original pair.

After three 90° bends from the straight to a right angle, the stretched came has begun to break.  The straightened came is deformed at the inside bend, but not broken. 

This test shows stretching the came to the extent that there is an "orange peel" appearance to the surface, dramatically weakens the lead came.  Only draw the lead came to make it straight, not to lengthen it.

When you are trying to get kinks and twists out, there is a point between straight and stretched where you begin to weaken the came instead of simply making it straight. There is a point in straightening linked or twisted lead that goes so far in trying to get it straight that the whole is weakened. When the orange peel appearance shows on the came, you have stretched to the weakening point. 

It is often better with kinked and twisted came to cut out the damaged portions and straighten the rest.

Lead Corrosion

There are three important versions of lead corrosion: Red, Brown and White.  In addition, there are other factors that can weaken the lead came.

Red lead is a corrosion product that appears as a bright red surface, is dangerous, and requires water, air and often wood, to form. Sometimes water in the manufacturing process can develop red lead.   The chemical composition of red lead (Lead (II, IV) or triplumbic tetroxide is Pb₃O₄ or 2(PbO^.PbO₂).  It is a bright red or orange crystalline or amorphous colour.

Red lead is virtually insoluble in water or in ethanol. But, it is soluble in hydrochloric acid as is present in the stomach.  When ingested, it is dissolved in the stomach’s gastric acid and absorbed, leading to lead poisoning. It also dissolves in undiluted acetic acid, as well as in a dilute mixture of nitric acid and hydrogen peroxide.

When inhaled, lead (II,IV) oxide irritates the lungs. In the case of a high exposure, the victim experiences a metallic taste, chest pain, and abdominal pain.

High concentrations can be absorbed through skin as well, and it is important to follow safety precautions when working with lead-based paint.

This means that anyone dealing with read lead needs protection against skin contact, and breathing protection.  Methods need to be implemented to ensure no dust is raised, or that the area is thoroughly cleaned after dealing with red lead. Clothing should be discarded or washed separately from all others.

White lead corrosion, Lead(II) carbonate, is the chemical compound PbCO₃. It occurs naturally as the mineral cerussite.  It is a curious compound, as it is soluble in both acid and alkali.  It is possible, but rare, for excess whiting left on the lead to give rise to this form of corrosion. Generally, it will be neutralised by the weather.

Brown lead corrosion appears as a brown to dull red colour. 

Lead(IV) oxide, commonly called lead dioxide or plumbic oxide or anhydrous plumbic acid …, is a chemical compound with the formula PbO₂. … It is of an intermediate bond type, displaying both ionic (a lattice structure) and covalent (e.g. its low melting point and insolubility in water) properties. It is an odourless dark-brown crystalline powder which is nearly insoluble in water. …. Lead dioxide is a strong oxidizing agent which is used in the manufacture of matches, pyrotechnics, dyes and other chemicals. It also has several important applications [e.g.,] in the positive plates of lead acid batteries.    Source: wikipedia

Air, water and salt are needed to form brown lead. This means coastal areas and those with driving rain are prone to this kind of oxidisation. Lead dioxide also forms on pure lead, in dilute sulfuric acid.  So, with the acid rain that we are all subject to, it can form in almost any situation, but will be more obvious on areas exposed to the prevailing wind.  The corrosion is soluble in strong acetic acid.

Tin corrosion also has a brown, almost copper appearance, very similar to brown lead.  The tin corrosion will be confined to the solder joint and surrounding area rather than all along the length of the came. 

Corrosion resistant lead

The ideal composition of lead to resist corrosion is 98.5% lead with up to 1% tin. This, combined with fractions of a percent of antimony and traces of silver, bismuth and copper provides a combination of metals and trace elements to resist corrosion of the lead as well as stiffening it.  Conservators indicate that, for whatever reason, cast lead incorporating trace elements is the most resistant to corrosion.  This is evidenced by the longevity of medieval lead cames.

Solder composition

Conservators also indicate that the higher the lead content of solder, and the better the match it is to the lead came, especially the almost pure lead came, the more resistant it is to lead came fracture at the margins of the solder joints.

Stretching the lead came, rather than simply straightening it, not only weakens the lead, it leaves very small pits in the surface of the lead.   These small pits allow the elements of the environment to penetrate the lead’s surface and act as sites for the beginning of corrosion.

Stretching also causes stress points near the solder joint.  The stretching creates stress along the length of the lead.  When the lead is heated in the soldering process the molecules of lead sort themselves into a stress-free arrangement.  As heat does not travel far or fast in lead, there is a stress point formed a short distance from the soldered lead joint where the already stressed and the stress-free lead meet.

Conclusion

Clearly there are a range of factors that relate to the resilience of lead came.  98.5% lead with trace elements including tin and antimony provides the greatest strength and resistance to corrosion.  Stretching the came can lead to general weakness and introduce pits into the surface forming sites for corrosion. Stretching can also lead to stress points near the solder joints.

All these indicate that resilient leaded glass windows can be produced by:

the use of lead came with 1.5% of trace elements,

the use of high lead content solders, and

the straightening (rather than stretching) of the came.

Stretching Lead Came

Stretching lead came is so ingrained into the literature and general thought that it is difficult to regain the purpose of the practice.  But I will try.

The purpose is to straighten the came

Purpose

The purpose of putting the lead into a clamp and pulling on the other end is to straighten the lead came.  It is much easier to work with a straight came than one that is curved or kinked.  It gives visually straight lines, it provides smooth and sinuous curves without interruption in the line of the curve.

It is said that some came is “pre-stretched”.  This is really the result of alloys contained in some lead to make it stiffer.  It still needs to be straightened before use.  If the lead came is already straight, you do not need to do anything else before using it.  If you drop or otherwise accidentally bend the came, you need to straighten it before continuing.

Stretching can weaken the came 

Stretching

Pulling on the lead came is not to stretch it, it is to straighten it. Stretching the lead can make it weaker. Lead drawn beyond its structural limits will break.  But you can weaken it before the break. You can test for this weakening of the came by observation. If you see "alligator" marks on the surface, you have weakened the came by putting too much effort into the pull. Straightening the lead must avoid so much force as to weaken the structure of the material.

Straightening not Stretching 

Straightening

The amount of effort to be put into straightening the lead came is just enough to make it straight. This will vary depending on how straight the came is at the start.  The reason for drawing the lead toward yourself is that you can see as you look down the length when the lead came is straight. If you are pulling vertically, it is more difficult to see when the lead becomes straight. 

If the lead is badly kinked or twisted, it may be best to cut that section out. If you continue to pull to straighten a difficult section, you can weaken the whole length of came.  First, ease the kinks and twists out as much as you can by hand. Then do an initial straightening pull.  This initial straightening pull will show where the problem(s) lie.  You can cut that section out and straighten the remaining pieces without stretching the lead to the point of weakness.

Safety

Of course, you must employ some basic safety rules.  Make sure the lead is securely clamped.  In the cleat style lead vices, you can give the lever a thump with the pliers to ensure the teeth are set into the lead before pulling on the other end.  Other vices need to have other ways to ensure that the end is held securely.

The other basic safety rule is that you should brace yourself against any break of the lead, or slip from the vice.  One foot should be placed behind you so that in case of breaks or slips you will not overbalance and fall.  This has the added advantage of ensuring you cannot put your body weight into the straightening effort.

There are other common sense rules, such as gloves, removing obstructions behind you, etc.

Conclusion

Remember that the purpose is to straighten, not stretch the lead came. 

If you are putting your foot on the bench to add force to the puilling of the lead in a vice on the bench, you are putting too much effort into the job and risk falling when the came breaks or slips out of the vice.  If your whole body weight is being used to draw the lead toward you, you are using too much force. If you can see signs of a pattern developing on the surface of the lead, you are using too much force.

Straightening the came is not an exercise in a workout programme.  It is a steady firm drawing force until the came is straight.  If you have to use more than usual force, stop and figure out why.  Cut out the difficult section so you do not weaken the came.  Then straighten the remainder and continue leading.

Polishing Brushes

The polishing brush should have moderately soft bristles. A long bristled shoe polishing brush can be used, although one that is a little stiffer does the job more quickly.

A shoe polishing brush

It is important to keep these brushes free of hardened cement, as a brush containing pieces of hardened cement will scratch the leads rather than darken them. As soon as the polishing is finished, inspect the brush for little balls of cement. Rubbing the brush against a clean rough surface will clean it while the cement is “wet”. Also running the brush at an angle on the sharp edge of your work bench will clear some of the cement adhering to the bristles.

A polishing brush with slightly stiffer bristles

If the cement hardens, you can clean the brush by crushing the hard balls of cement with a pair of pliers. Or you can just get a new shoe polishing brush.

Encapsulation of Fused Glass Panels

You can encapsulate both leaded and fused glass panels into double glazed units.

Leaded glass panels have the outer came built in “Y” shaped came.  The tail of the “Y” is held between the spacer bars at the edge of the double glazed unit. You normally need to leave 25mm space on each side.  It is calculated as the reduction from the glazing size of the opening.  This is required to accommodate the width of the heart of the came, the spacer bars and sealant of the double glazing assembly.

The same sizing guide is required for fused glass panels.  Usually the “Y” came is designed for 3 mm glass, as it has a 5mm high heart.  However, the “Y” is broad enough that the leaves can be opened to accept the thicker 6mm fused glass.  It is also possible to grind a bevel on the back of the fused glass to make it easier to slip into the came.

It is best to find the person or company which will be making the double glazing unit before starting.  Discussion with them at the start will enable you to determine how much allowance is needed for the spacer bars and the sealant. This will assure you in setting the dimensions for the panel you will make.

Storage of Came

There are a variety of ways of storing lead came.  The best would be storage in air tight containers.  In the absence of that, many solutions are possible.  These are some of the considerations you should be thinking of when constructing your came store.

Straight

You will get the most use from your came if you store it straight.  If you are short of space or don’t have long arms to handle both ends at the same time, you can halve the normal 2 metre lengths. This also makes for shorter storage units.

Container

The surface oxidisation of lead is reduced by keeping it in a container whether box or rainwater pipe for example.  If the ends or top is open, it is a good idea to wrap the came in waxed paper, as that seems to keep the lead better than ordinary paper.

         

Dry

Lead oxidises on the surface quickly in a damp atmosphere. Try to store it in an area that is not subject to condensation.

Ease of extraction

When building your container, think about how easy it will be to extract the lengths of lead, whether by drawing or lifting them out.

The rate of surface oxidisation relates to the purity of the lead.  The more pure the lead the quicker the surface oxidises.  Half hard and hard cames oxidise more slowly.  However it is normal to have to make sure the surface is bright before soldering.  Don’t worry about a bit of oxidisation – it is only the surface and a scrubbing with a brass wire brush at the joints will have the came ready for flux and solder quickly.

Plating

Objective

The object of plating is to modify the original colour, either by changing the tone or the intensity. This will, for example, darken a piece of glass where it would otherwise be to bright; or it will modify the colour to better blend with the surrounding pieces.

A further use of plating is in conservation, where the additional detail is placed on a separate piece of glass and placed in front or back of the original.

Leads

In leading, you normally use high heart lead. This is lead with a heart of 7mm or 10mm instead of the usual 5mm. Other heights are available, of course. The 7mm heart will accommodate two 3mm pieces, but if you are using thick hand made glass, you may require the 10mm high heart.

Comparing the Arrangement

Try the glass combination with each piece on top. Often there is a difference in tone or texture. Choose the one that suits your composition best.

Cleaning

Before finally fixing the glass together, make sure they are very clean as there will be no opportunity to clean the inside again. Try to avoid finger prints on the insides while you do further work with the glass.

Sealing

Make sure the glass fits the cartoon lines. You will be sealing the two pieces of glass together, so there is no opportunity to change the shape later. There are a variety of traditional methods of sealing the glass, but the easiest modern approach is to copper foil the edges to ensure that no cement creeps between the pieces.

Fitting

You then fit the glass into the came as for thiner pieces. Where you have a combination of heart heights, you can simply slip the ends of the lower heart cames inside the leaves of the high heart leads. The differences in height are small enough that no special support is needed for the thinner glass unless you feel better with the single layers of glass supported above the work surface.

Lead Corrosion in Acids

Lead forms a protective film, which if undisturbed preserves the metal below this layer.

The corrosion resistance of lead is based on its ability to readily form a tenacious coating of a reaction product. This then becomes a protective coating. Protective coatings on lead may form as the result of exposure to sulphates, oxides, carbonates, chromates, or chemical complexes.

Handbook of Corrosion Data, by Bruce D Craig, p26

Lead is resistant to corrosion especially “with solutions containing sulphate ions, such as sulphuric acid.”

However, the new or bright metal reacts quickly with a variety of alkalis and many organic (although not most inorganic) acids.  “...Lead is not stable in nitric and acetic acids, nor in alkalis. The metal does not resist nitric acid. Lead corrodes rapidly in acetic and formic acids.” (Handbook of Corrosion Data, by Bruce D Craig, p.29)

Lead has very limited resistance to acetic acid.... Dilute [acetic acid], even at room temperature attacks lead at rates exceeding 1.3mm/year. These rates increase rapidly with increasing aeration and velocity However … acetic acid … has little effect at strengths of 52% to 70%.

The corrosion rate in acid increases rapidly in the presence of oxygen and also in oxygen in combination with soft waters such as rain and distilled water. Corrosion increases at the rate approximately proportional to the oxygen content of the water.”

Handbook of Corrosion Data, by Bruce D Craig, p.26, 29

This another good reason to avoid vinegar as a cleaning agent for leaded windows.

Lead dissolves in organic acids (in the presence of oxygen). Lead also dissolves in quite concentrated alkalis (≥10%) because of the characteristic of the lead salts that can act as either an acid or an alkali. These salts are soluble in the presence of water and oxygen.

Alkali salts are soluble hydroxides of alkali metals and alkali earth metals, of which common examples are:

• Sodium hydroxide (often called "caustic soda")
• Potassium hydroxide (commonly called "caustic potash")
• lye (generic term, for either of the previous two, or even for a mixture)
• Calcium hydroxide (saturated solution known as "limewater")
• Magnesium hydroxide is an example of an atypical alkali since it has low solubility in water (although the dissolved portion is considered a strong base due to complete dissociation of its ions).

Although this has been a rather technical posting, these data show that lead is subject to rapid attack by both organic (and some inorganic) acids and alkalis in relatively low concentrations when in the presence of aerated water. However in normal environmental conditions the protective reaction layer avoids much of this vulnerability.

Installing Leaded Glass in Stone

Side rebates
One side of the rebate (or raggle) in stone should be deeper than the other. This allows the panel to be slotted in and then slid back into the shallower rebate. Which side the deep rebate is on is not important, but you must determine which is the deeper and its minimum depth all along the raggle.

Adjusting the placement of the panel
To help move the panel from side to side stiff oyster knives and lead knives are important. This allows you to get behind the edge and slide the panel to the side, especially when it is sitting on top of another panel to make the fine adjustments to get the lead lines flow correctly.

In some circumstances, especially when installing a single panel, it is necessary to bend the leaves of the lead toward the installation side. After placing the panel, you then fold the leaves out one at a time into the raggle slot.

Top and bottom rebates
For the top and bottom rebates it is important that the top is the deep one. You insert the panel up into the slot a the top and let it settle into the bottom rebate. The panel should be completely covered by the stone.

Extra came
In all installations into stone, you should carry extra came of at least 12mm (1/2”) to solder round the panel when the stone work is not as accurate as it should be, either through workmanship or weathering.

Wedges
Have some little blocks of wood and some whittling tool to hand to wedge the panel in till mortared. It is possible to use little scraps of lead for the purpose. These wedges don't need to be that robust, they are just there to hold the panel in place until the mortar is in.

Mortars
Mortars for stone should be of lime cement, or sand mastic. Don't use silicon, you'll never get it out again! Also don't use putty as this stains some types of stone and the oils leech in to the stone, causing the putty to dry and therefore the window ceases to be watertight.

Lead Came with Alloys

Lead came is available in several hardnesses. One (soft) is almost pure lead, another is half hard and contains up to 5% antimony, and the third is hard, containing up to 10% antimony. The difference between these is hardness, or resistance to creep, not resistance to corrosion.

elemental lead

Lead with antimony as an alloy is subject to the same corrosion rate in atmospheric environments as chemical lead (99.9% commercial-purity lead). However the greater hardness, strength and resistance to creep of antimonial lead often makes it more desirable for use in specific chemical and architectural applications.

The ability of some antimonal leads to retain this greater mechanical strength in atmospheric environments has been demonstrated in exposure tests in which sheets containing 4% Sb [antimony] and smaller amounts of arsenic and tin were placed in semi-restricted positions for 3 years. They showed less tendency to buckle than chemical lead, indicating that their greater resistance to creep had been retained.

Handbook of Corrosion Data, by Bruce D Craig, p89ff

Antimony crystals

Thus, the use of softer leads in conservation or restoration, because they were used in earlier periods, is not indicated. It is known that lead came up to sometime in the early 19th century was melted and re-formed into came, incorporating tin from solder and other trace elements which made the lead “stiffer” than the more pure lead that began to be produced commercially and used widely at that time. This may be the reason that so many 19^th century windows contain failing leads, while many earlier ones remain sound.

Bending Wide Cames

The way to bend larger leads such as flat outside leads around pieces of tracery or other curved shapes in window panels is to lay the lead upon the bench, and use a curved, preferably wooden, lathekin.

Progressively manipulate the lead into the curve. Hold the lead steady by keeping your fingers spread on the top and back of lead and manipulate the curve between your extended fingers. Gently push the curved lathekin along the heart of the lead with small, smooth, circular strokes. Smooth the lead flanges by pressing down on the flanges on the inside of the curve as you go. If you try to do it too quickly the lead will probably buckle.

Frequently turn the lead over, applying the process to both sides.

If the flange crimps or buckles, put smooth jawed pliers inside the lead and squash the flange flat. The pliers can be used to flatten any kinks that develop in the lead.

The key is to handle the lead gently and in stages, gently flattening the complete lead and not flattening completely one spot before moving on to the next.

The advantage of round over flat in this circumstance is that round came of the same size can be bent into smaller curves that the flat came of the same width.

The technique for finishing a curve around a single piece of glass can be seen in the tip “Leading Small Circles”

Lead knives

The advantage of lead knives over lead dykes are that a wider variety of angles can be made with the knife. There are a number of varieties of lead knives - ranging from adapted paint scrapers to specially made sophisticated tools.

The technique in using a knife is to wiggle or rock the blade with some moderate pressure down through the lead came. Excessive pressure will twist the came rather than cut it cleanly and squarely. When you find the effort or time required to cut through the came has increased, it is time to sharpen the blade. The sharpening angle should be very acute. You can use a fine oil stone or wet and dry sand paper to hone the cutting edge. You can also use a little bit of wax or soap on the blade to ease its passage through the came.

The most simple knife is a stiff paint scraper. The blade should be of good steel so that it takes and retains the sharpening that is needed from time to time. This blade works best by wiggling through the came.

Another style of lead knife has a curved blade. This has a number of variations. This knife works both by wiggling and by rocking.

Experience and personal preference will determine which style you settle on. The important elements are to make sure it is made from good steel and that it fits your hand comfortably.

You can add a metal end to the handle to provide a tool with more uses, especially as a hammer to put the nails into the board, or to snug up wooden borders, sometimes even gently tap the glass into place.

Also look at the use of lead dykes.

Leading Nuggets

To use nuggets in leaded glass panels, just wrap the came round the nugget. If the came leaves are oval, it works better than the flat. If the nugget is thick and does not want to fit securely in the channel, you can also use a fid to open up the top leaf of the came.

There also is a technique to cut the came to give a smooth curve given here.

Bulging lead panels

There is probably no means by which leaded glass, because of the innate character of lead as its skeleton, can resist its propensity to bend, bulge and sag. Evidence of these occurrences does not necessarily foretell disaster or immediate collapse. Bulging does not necessarily indicate the need for action or re-leading.

There are three basic stages through which stained glass passes on the way to requiring repair;
1. Bulging, bending and sagging
2. Loss of putty and breaking of solder joints
3. Unhousing of the glass from the lead


The points at which solder joints break depends on the materials used.

Since lead, compared with solder, is a resilient material abutting the more resistant solder, breaks will occur most frequently at the junction of the solder with the lead.

With zinc, the situation is reversed. The zinc is of greater resistance than the solder. As a result the break most often occurs on the solder at the point of the zinc junctions.

It is the very existence of resilience in lead which responds to the expansion and contraction of glass that permits the more healthy survival of the glass over the less sympathetic accommodations of either zinc or copper foil. Leaded glass, unlike any other medium, has the unique capability of having its skeleton (lead) replaced, when the need arises, without damaging its body (glass).

Butting of leads

Lead came is normally cut to meet up against the adjoining cames. This provides a neat joint that will carry the solder without needing to fill gaps. The easiest joints to make are those at right angles. You can measure or estimate the amount that the came must be shorter than the glass, but it is easiest to use a piece of came the same size as will be passing the piece you are cutting (gauge came). You centre the gauge came on the cartoon cut line near the joint. Using your lead knife you can extend the line of the side of the gauge came to the piece you will be cutting. The mark you make with the lead knife can then be used to guide your cut of the came, as you take it away from the glass.

Those joints with angles have the came marked and cut in the same way as for right angles as the gauge came will give you the correct angle to cut.

Always remember when leading that you lead to the cartoon lines not to the glass. If the glass is short, use the cut line to place the gauge on, not against the glass. If the glass is too large, adjust its fit.

Dressing the Lead Came

If you have consistent difficulty in sliding the glass into the came, you should consider dressing the came before use. Dressing the came consists of running a fid or other hard material along each of the four flanges of the came. In doing this, you are pressing each flange in turn down against the bench or other smooth surface.

Dressing the cames gives a slight bevel or ramp for the glass to slide over the edge of the came and into the channel of the came. You can dress the whole length at once, or as you cut the pieces off from the main length. Dressing shorter pieces is less likely to bend the came.

Lead Came

Lead came is often just called came. There are two basic types of lead: hard lead and soft lead.

Soft lead is 100% pure lead with nothing added. Soft lead strips need to be straightened in order to remove the propensity to stretch and sag. The advantage of soft lead is being easier to bend and shape to curves and that straightening removes any kinks in the length. Within 50 years it will need to be replaced.

Hard lead has antimony added which stiffens the lead. This results in a stronger finished panel. However this kind of lead deteriorates relatively rapidly. The advantage of hard lead is the added strength and not having to stretch it. It will need to be straightened just before use though. It is still malleable enough to conform to most curves.

Came is available in many shapes, although H, U and C are the most common. The lengths are usually about 2 meters (6 feet). C and U shaped lead is used on the outside of a panel. H shaped lead can be used on both the interior and edge of a panel.

The came’s top and bottom are the flanges and the width of the flange is the nominal size of the lead. These flanges can be flat (parallel surfaces) or rounded (a slight dome on each of the flanges). The central part of the came is called the heart, normally 1.2mm (1/16”) thick.

Framing Panels with lead

One option for framing, especially where the edges are not rectangular is to use lead. The lead touching the glass or copper foiled edge should be 10mm flat came. This allows you to insert a 5mm mild steel rod shaped to the outside of the panel. This is then covered by a 13mm flat came. The came is smoothed by gentle pressure on the upper and lower flanges with a stopping or lead knife to bring the two flanges together. This gives a pleasant finish to the edge.

by Gene Mallard

Fixing the Final Perimeter Cames

When all interior leads are in place, the top edge came is cut to butt against the vertical side edge, using a small piece of lead the same size to act as a gauge. These edge cames should butt up to the came ends in the interior.

Place a narrow strip of wood against the top outside came and hold it in place with horseshoe nails. Check with a square or by measuring to be sure the just placed came is at right angles to the left side of the panel. Do the same with the other side.

If adjustment is necessary, firmly tap the wood batten with the hammer end of your lead knife to get it into position. Place nails to hold the cames in position and get ready to solder.