Zinc Health and Safety

So much is said about the toxicity of zinc, I thought to look up some facts.

As there is significant concern about health issues, it is useful to look in detail at the health and safety issues around the use of zinc at elevated temperatures.  Zinc is absorbed into the body by inhalation of fumes and consumption of zinc containing materials.

Toxicity

Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption … [which results in the symptoms of zinc intoxication].  Stomach acid contains hydrochloric acid, in which metallic zinc dissolves readily to give corrosive zinc chloride. … The U.S. Food and Drug Administration states that zinc damages nerve receptors in the nose, causing [loss of smell].

Evidence shows that people taking 100–300mg of zinc daily may suffer induced copper deficiency. … Levels of 100–300mg may interfere with the utilization of copper and iron or adversely affect cholesterol. … A condition called the zinc shakes or "zinc chills" can be induced by inhalation of zinc fumes while brazing or welding galvanized materials. 

https://en.wikipedia.org/wiki/Zinc

Poisoning

Consumption of zinc can result in death, but requires large amounts (over 1 kg in one case).  Smaller amounts result in lethargy and gross lack of coordination of muscle movements or apparent intoxication. https://en.wikipedia.org/wiki/Zinc

Research and W.H.O. Information

The Essential Toxin: Impact of Zinc on Human Health, by Laura M. Plum, Lothar Rink, and Hajo Haase^*

Compared to several other metal ions with similar chemical properties, zinc is relatively harmless. Only exposure to high doses has toxic effects, making acute zinc intoxication a rare event. In addition to acute intoxication, long-term, high-dose zinc supplementation interferes with the uptake of copper. Hence, many of its toxic effects are in fact due to copper deficiency. While systemic [balance] and efficient regulatory mechanisms on the cellular level generally prevent the uptake of [cell destructive] doses of [environmental] zinc, … zinc [within the body] plays a significant role in cytotoxic [death of individual cells] events in single cells. … One organ where zinc is prominently involved in cell death is the brain, and cytotoxicity in consequence of [inadequate blood supply] or trauma involves the accumulation of free zinc.

Rather than being a toxic metal ion, zinc is an essential trace element. Whereas intoxication by excessive exposure is rare, zinc deficiency is widespread and has a detrimental impact on growth, neuronal development, and immunity, and in severe cases its consequences are lethal. Zinc deficiency caused by malnutrition and foods with low bioavailability, aging, certain diseases, or deregulated homeostasis [equilibrium] is a far more common risk to human health than intoxication.

Conclusions

Zinc is an essential trace element, and the human body has efficient mechanisms, both on systemic and cellular levels, to maintain [balance] over a broad exposure range. Consequently, zinc has a rather low toxicity, and a severe impact on human health by intoxication with zinc is a relatively rare event.

Nevertheless, on the cellular level zinc impacts survival and may be a crucial regulator of [the death of cells occurring as a normal and controlled part of an organism's growth or development]  as well as neuronal death following brain injury. Although these effects seem to be unresponsive to nutritional supplementation with zinc, future research may allow influencing these processes via substances that alter zinc [balance] instead of directly giving zinc.

Whereas there are only anecdotal reports of severe zinc intoxication, zinc deficiency is a condition with broad occurrence and potentially profound impact. Here, the application of “negative zinc”, i.e., substances or conditions that deplete the body of zinc, constitute a major health risk. The impact ranges from mild zinc deficiency, which can aggravate infections by impairing the immune defence, up to severe cases, in which the symptoms are obvious and cause reduced life expectancy.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872358/

Zinc came
Credit: leadandlight.co.uk

World Health Organisation Document

10.2.2 Occupational exposure

Occupational exposure to dusts and fumes of zinc and zinc compounds can occur in a variety of settings in which zinc is produced, or in which zinc and zinc-containing materials are used. Typical airborne exposures observed include 0.19–0.29 mg/m3 during the smelting of zinc-containing iron scrap, 0.90–6.2 mg/m3 at non-ferrous foundries and 0.076–0.101 mg/m3 in hot-dip galvanizing facilities. Far higher exposures are possible during particular job activities, such as welding of zinc-coated steels in the absence of appropriate respiratory protection and/or fume extraction engineering controls.

Occupational exposure to high levels of zinc oxide and/or nonferrous metals is associated with metal-fume fever. [a condition in which the sufferer has influenza type symptoms - a raised temperature, chills, aches and pains, nausea and dizziness. It is caused by exposure to the fume of certain metals - commonly zinc].  This is usually a short-term, self-limiting syndrome…. Induction of metal-fume fever is most common with ultra-fine particles capable of deep lung penetration under conditions of exposure. Studies on volunteers conducted under short-term exposure conditions (77–153 mg/m3 for 15–30 min) have detected pulmonary inflammation responses (including [inflammation] induction) which are consistent with manifestations of metal-fume fever and support an immunological [cause] for this acute reversible syndrome.

Evaluation

Based on the available information, it is not possible to define a no-effect level for pulmonary inflammation from exposure to zinc oxide fume.

10.2.4 Risks of zinc excess

Toxic effects in humans are most obvious from accidental or occupational inhalation exposure to high concentrations of zinc compounds, such as from smoke bombs, or metal-fume fever. Modern occupational health and safety measures can significantly reduce potential exposure. Intentional or accidental ingestion of large amounts of zinc leads to gastrointestinal effects, such as abdominal pain, vomiting and diarrhoea.

In the case of long-term intakes of large amounts of zinc at pharmacological doses (150–2000 mg/day), the effects (sideroblastic anaemia [inability to make haemoglobin], leukopenia [low white cell quantities] and hypochromic microcytic anaemia [iron deficiency]) are reversible upon discontinuation of zinc therapy and/or repletion of copper status, and are largely attributed to zinc-induced copper deficiency.

High levels of zinc may disrupt the [balance] of other essential elements. For example, in adults, subtle effects of zinc on copper utilization may occur at doses of zinc near the recommended level of intake of 15 mg/day and up to about 50 mg/day. Copper requirements may be increased, and copper utilization may be impaired with changes in clinical chemistry parameters, but these effects are not consistent and depend largely upon the dietary intake of copper. Distortion of lipoprotein metabolism and concentrations associated with large doses of zinc are inferred to be a result of impaired copper utilization. In groups with adequate copper intake, no adverse effects, with the exception of reduced copper retention, have been seen at daily zinc intakes of [less than] 50 mg/day. There is no convincing evidence that excess zinc plays a [casual] role in human carcinogenesis. The weight of evidence supports the conclusion that zinc is not genotoxic [damaging of genetic information in cells] or teratogenic [affecting the development of embryos]. At high concentrations zinc can be cytotoxic [toxic to cells].   https://www.who.int/ipcs/publications/ehc/221_Zinc_Part_3.pdf?ua=1

zinc sheet 
Credit: Belmont Metals

Use and Risks of Zinc in Kilnforming

Zinc melts at 420°C and boils at 907°C, so any fumes will be emitted only around and above the full fusing temperature of glass.

The main problem in kilnforming is that the metal melts at such a low temperature that it is not useful for containing the glass.

There is anecdotal evidence to indicate that firing zinc contaminates the kiln, leading to subsequent devitrification issues.  This can be cleared by firing bentonite at high temperature in the kiln to absorb the zinc.

It is not a high-risk metal, even if it were to vaporise (above 900°C).

Research papers show zinc poisoning to be extremely rare. It is usually associated with taking too large daily doses of zinc as a dietary supplement, or swallowing USA pennies - made largely of zinc - which dissolves in stomach acid and creates large problems for the digestive system.  Where zinc intoxication occurs, it is largely reversible.

Conclusion

The idea that zinc will poison you in kilnforming conditions is simply not correct.

Removing kiln wash from moulds

“How do I remove kiln wash from a mould that I have decided would work better with ZYP?”

Once coated with kiln wash, slumping or draping moulds do not need to be re-coated until the surface is damaged.  Then it is best to remove all the kiln wash to prepare a new smooth surface for the kiln wash.  You may, of course, as the enquirer above states, want to use a different kind of separator.  The cleaning of the kiln wash from the mould will be the same process whatever you want to do with the mould next.

There are many ways to get the old kiln wash off.  Some of them depend on the material from which the mould is made.

Metal

If the mould is made of stainless steel or other metal, the easiest method is to sandblast with lots of air and a minimum of grit.  You can also use sandpapers or open weave sanding screens. The methods used on ceramic moulds, as described below, can also be used on metal.

Ceramic

Sandblasting is not safe to use on ceramic moulds, as the sandblast medium can erode the surface very quickly and often unevenly.

Preparation for manual removal of kiln wash.

It is best to wear a mask during this process to reduce the amount of dust you inhale. Spread a cloth, newspaper or other covering to be able to easily gather the removed kiln wash and place it in the waste.  Have a vacuum sweeper at hand to remove powder rather than blowing it around the work space.  Of course, if you can do this outside, there is much smaller risk of contamination.

Dry

I suggest that removing the kiln wash while the mould is dry should be the first stage. 

Flat surfaces can be cleaned with a straight edged wooden stick, or wooden clay modelling tool.  Firmly push it along at a slight angle from the vertical to remove most of the kiln wash. 

On curved surfaces you will need a rounded tool such as a plastic burnisher or all nova tool for the coarse work.  This can be followed up by using a stiff sponge to clean up any stray kiln wash still adhered. If the kiln wash is persistently sticking to the mould, you can cut a small piece from an open weave sanding screen and use it to gently remove the most difficult remaining kiln wash.  Do not use more than light pressure, as with heavy pressure, the screen can begin to remove the surface of the ceramic mould.

Texture moulds and those with a lot of detail or right-angle corners need a bit more attention.  You can use a variety of non-metal tools to get into areas of detail.  Some of these are a rounded chopstick, a wooden skewer, a plastic knitting needle, and other similar items with rounded points.  These can be backed up with a small stiff nylon brush.  It is while working on these detailed areas that the vacuum sweeper will be most useful to clear out the debris and enable you to see how well the kiln wash is being removed.

Wet

Some people do not like the idea of the dust created from the removal of the kiln wash being in the air at all.  And sometimes, the dry removal is not complete.

My recommendation is to dampen the kiln wash that is on the surface of the mould.  This will cause some difficulties in removal, because a slurry is created along with the flaking of the baked-on kiln wash.  The same tools can be used to clean the mould as when dry.  The vacuum sweeper will not be of use though.  Once the kiln wash appears to be cleaned away, the mould needs to dry to enable removal of the remaining kiln wash.  Once dry, you can use dry sponges, or the small nylon brush to clean the remaining film of kiln wash from the mould.  This cleaning may reveal areas where the kiln wash is still adhering. These can be dealt with wet or dry, although I prefer dry.

Soaking or washing the mould does not remove the kiln wash as easily as you might think.  It is especially to be avoided where the mould has an internal hollow, as it may take days to dry sufficiently to apply other separators.  To put it in the kiln risks breaking the mould by the steam build up during the initial rise in temperature.

If you must soak the mould, I recommend that you use a 5% solution of citric acid because it has a chelating action on some of the components of kiln wash.

Remember that once the mould or shelf has been coated with boron nitride, it is almost impossible to go back to kiln wash again.  The boron nitride fills the porous parts of the ceramic making it difficult for the kiln wash to adhere to the mould.

Further information is available in the ebook: Low Temperature Kiln Forming.

Materials for making dams

Rectangular or straight sided shapes

Broken shelves

Accidents happen to mullite shelves causing breaks or cracks.  Rather than throwing them out, you can cut them into rectangles or 50mm strips with a tile saw.  The resulting shapes need to be kiln washed to keep glass from sticking.  They can be used flat or stood on their edges with supports on the outside.

Thick ceramic tiles can be used in much the same way.  You do need to remove the glaze from the tile to make sure they don’t stick to the glass.  Or you could use the unglazed side toward the glass. Again, the tiles need to be kiln washed.

Stainless steel can be used as a dam.  It will need treatment with a separator such as boron nitride or kiln wash.  In addition, it needs to be lined with refractory fibre paper to cushion the force of the greater contraction of steel than glass.

These materials cannot easily be adjusted in length to fit the size of the glass piece being dammed.  Instead, arrange them in a swastika like formation. 

This photo also shows how shorter lengths can be incorporated to make the whole dam.

Vermiculite board is a refractory material that can be used to form dams by cutting with a wood working saw.  The saw you use to cut the vermiculite will be dulled and only be useful for cutting vermiculite in the future.  Do not use any expensive cutting equipment!  

Credit: Bullseye Glass Company

Refractory fibre board is available in many thicknesses.  It can be cut with craft knives even though it dulls the blades quickly.  The thicker boards can be used without rigidising.  This avoids the need to kiln wash and allows adjustments in length.  If you do rigidise fibre board, you must coat it with a separator such as kiln wash or boron nitride.

Weighted fibre paper can be used.  It is sometimes the quickest and easiest to use, as there normally is a stash of scraps around the studio.  It is easily cut with a craft knife.  You can build up the thickness of the dam by layering pieces on top of one another.  Sometimes people put metal wire or pins in the layers to ensure there is no movement between the layers. I’ve found that if weighted, the fibres interlock enough that the layers do not shift.  But you need to line the layered fibre paper dams with vertical strips of fibre paper, so the glass does not take up the layered dam profile on its edge.

Note that you need to use breathing protection when cutting all these materials.

Curved and circular pieces

Many times, the shape to be dammed is not formed of straight lines.  Different materials need to be used in these cases.

Formed stainless steel is a good durable and reusable material.  You need to line the shape with fibre paper if it completely contains the shape, because it contracts more than the glass and can crush the piece.  It is expensive to have made and so needs to have multiple uses to justify the cost.  A cheaper alternative is to make your own shape using stainless steel strapping as used for shipping crates and pallets. 

Fibre paper is an excellent material for damming irregular shapes.  It can be cut into complicated shapes, and it can be layered to attain the required height. You can weight it if you are taking things to a high temperature and fear that the glass will flow under the fibre paper.

You can also use the thicker fibre papers upright by backing up with multiple pieces of kiln furniture to maintain the shape you desire.

Vermiculite board is a good material for making shapes, although not as complicated ones as possible in fibre paper.  Vermiculite can be shaped with wood working materials, but cheap ones should be used as they are quickly dulled. You can rough out a shape with a jigsaw and refine it with various wood working tools, including coarse sandpaper.  Because it is a relatively rigid material, a lot of inventiveness can be used in forming the edges by altering angles from the vertical, incising designs into the edge, etc.  Be certain that you have adequately kiln washed or put other separator on the board, as it will stick to the glass if left bare.

Fibre board is a less rigid material than vermiculite, but is easier to work with simple craft tools.  It is simple to use for a unique one-off shape. It only needs smoothing and does not have to have a separator applied because it does not stick to the glass.  If you create a shape that you will want re-use, you can rigidise the board after shaping, but it will require separators then.

Note that when working with refractory materials, you need to wear respiratory protection and clean surfaces with a HEPA vacuum or by dampening dusty surfaces and wiping them clean.  Dispose of cleaning materials safely.

Rakes for Combing

It is of course, possible to buy commercial tools for combing hot glass.  But with a little ingenuity, you can make your own for a small amount of money and some effort.

My raking tool is a metre long round stainless steel rod, 8mm in diameter. I sharpened it on a  grinder for metal rather than my glass grinder. Then I bent a right angle to give me 75mm "hook". The handle is a piece of broom handle. I drilled an 8mm hole in the wood and hammered it on.

A longer metal and shorter wooden handle works better than the one I made with a long wooden handle, as there is no wood near enough the heat to burn. If you do have a long handle,  soak it in water to keep it from burning.

It is possible to make a rake using mild steel rod, but it is more likely to spall and drop flakes into the glass.  Both metals need to be kept cool.  Rest the rake in a bucket of water before the first pass at combing.  As the glass stiffens and you need to wait for the glass to come back to a combing temperature, put he rake back into water to cool it.  If you try to comb with a hot rake, it will stick to the glass.

It is important to have a handle made of an insulating material to avoid any possible electrical shocks.  It also makes for a more comfortable handle that does not heat up.

Safety gear is required to protect eyes and clothing from the heat.  It is not possible to have the kiln open at around 900C without it.  This is the face, hand and arm protection I use.  The coated visor protects your eyes against the infrared radiation from the kiln.  The gloves can be the aluminised silver colour ones or the kevlar ones.  The alminised ones are easier to manipulate things with.  The arm protectors are aluminised too. They are easy to put on and give additional safety to the body.

Natural fibres should be worn to avoid clothing bursting into fire.  I use a denim jacket reversed for additional chest protection.

Soldering old lead

This is normally only a requirement when repairing old windows. Usually either to join new lead to the old, or to repair breaks at the original solder joint.

You will need to clean the lead down to the bright metal at the joints. This is more than a rub with steel wool. You need a glazing nail to scratch through the oxidisation layer, the corner of your lead knife, or in cases of mild oxidisation, a brass wire brush might do. But not a steel one as that may scratch the glass and any painting.  

Do not clean the oxidisation off the lead elsewhere. That is a protective layer already formed which leads to the longevity of the came. It is best to leave oxidised lead alone rather than expose the metal to further oxidisation.

Getting to the bright metal where you want to solder the joint means the flux can act appropriately and help the solder form a secure joint.  Otherwise only a weak, cold joint is possible.

Note that you always need to use dust masks or other breathing protection.  You need to have the work area well ventilated and need to do a damp wipe down of surfaces to reduce the amount of lead oxide in the work space.

Fibre Dams

Fibre dams are a good and relatively inexpensive refractory material to form dams around regular and especially irregular shapes.  You need only cut the shape you want from the fibre board, if it is not a shape with straight lines.  

You can fire without any kiln wash or hardening if it is a one-off use.  For shapes you want to keep, you can harden the fibre board. 

Once hardened with colloidal silica, you need to paint the board with a separator – kiln wash, boron nitride or similar.

There are some precautions in the use of fibre paper and board.  The main physical one is that refractory fibre is lighter than glass and so will float on top of “molten” glass – that is fusing compatible glass higher than about 800°C.

Fibre board dams can be weighted with kiln furniture on the surface of the board.  If the board is flat this can be on the surface.  If the board is vertical, weights can be placed at the corners.

In the absence of fibre board, you can use layers of fibre paper.  If you have 6mm fibre paper, you need only one layer for two-layer glass, but remember that to get a bullnosed edge to the glass without needling, the fibre paper should be 3mm less than the final height of the fired piece. Thicker glass will require more than one layer of fibre paper.  Place as many layers of fibre paper as required to be at least equal in height to the finished piece on top of one another.  Push “U” shaped pins into the layers of paper to fasten the layers together.  Then cut the required shape out of all the layers all at one time. 

When finished cutting the shape out, you may want to line the edge with 1mm fibre paper to keep any of the layers of fibre paper showing through.  This dam will not need any kiln wash to prevent the glass sticking to it, unless you want multiple uses and so need to rigidise it with colloidal silica.

You can weight this fibre paper dam down by placing kiln furniture near the edge, all around the shape just as for the fibre board.

Safety in use of refractory fibre is described in Gregorie Glass.

Scroll down to Dusts/Particulates for safety recommendations.

Peeking

Observation is desirable for learning and essential for several processes.  How you do that is important to the safety and health of your eyes and skin.  This post gives some guidance on the protections required.

Each observation should take a fraction of a second. It is called peeking to distinguish it from looking or watching. There is a method to doing this. Think about what you are looking for before you open the kiln. Pop open the kiln to record with your eyes, close the kiln. Think about what you saw. If necessary, repeat.  But only after you have thought about what you saw.

Do not spend time looking into the kiln.

Think about the necessity for observation before buying your first or next kiln. 

The best kilns are those with generous observation ports, both in number and size.  These allow you to peek into the kiln without disturbing the heat distribution within the kiln.  Two or more ports are best, as you can shine a light into one of them to illuminate the interior of the kiln at lower slumping temperatures.

If you do not have ports you will need to open the kiln. This is easiest to do with top hat kind of kiln.  The top hat kiln keeps a lot of heat in the upper portion of the lid, making the amount of heat dumped less than on other kinds of opening.  You can peek in at the level of the shelf, so minimising the amount of heat being dumped.

The problems with lids opening so you have to peer down into the body of the kiln, and with doors opening to the front, is that you are dumping a lot of heat directly at yourself.  You also are losing a significant amount of heat from the kiln.  The large air exchange also will disturb any dust in the kiln and that may fall onto your work.

It is possible to make ports in your kiln by drilling a large diameter hole in the side of the kiln and through the insulating material (assuming you do not have side elements).  This post gives some ideas.

In all the cases where it is necessary to open a lid or door, you must close the kiln slowly and gently to minimise disturbance of the air within the kiln.

The effects on the glass of peeking at various temperature ranges varies between the rise and the fall in temperature.  This post 

gives some ideas of the effects.

Soldering Fumes

Exhausting Soldering Fumes

Health and Safety

The health and safety of working with lead and solder are a great concern of many people.  Greg Rawls, the acknowledged expert in glass working health and safety, puts soldering and lead work in perspective.

Soldering lead came for stained glass does not usually present an inhalation hazard if the area is well ventilated and you are using an iron and not a torch. With normal soldering, you are melting the lead at temperatures that are NOT hot enough to create a fume.
Lead fume is the inhalation exposure issue. Fumes are very small respirable particulates that are made with heat. Liquid chemicals give off vapours.

Avoid exposure by ventilating the area when soldering, especially if using a torch instead of an iron. Open a window and turn on a fan!  Wash your hands thoroughly when finished working with lead. There are specific products for this purpose.

Use a P95 or P100 respirator when concerned about lead exposure. 

http://www.gregorieglass.com/chemicals.html

There are commercially made fume traps which often have an activated charcoal filter and can be effective.  A simple desk top fan blowing away from you can be effective in well ventilated areas, if you are working on your own. (otherwise it blows the smoke toward others.)

An example of a fan drawing fumes away from the person soldering

Making a fan

Exhausting fumes while soldering is a safety issue. If you happen to have an outdoor screened-in studio a simple fix can be had with a computer fan! You can scavenge such a fan from an older used computer ready for disposal. Simply cut four timbers 50mm square or 25mm x 100mm to fit around it as a box. Attach a long electrical cord to it with an approved plug. Attach a screen to both sides. Plug in. An additional feature is to attach an activated charcoal filter (as used for cooker hoods) to the front of the fan. This removes particles and some fumes.

Positioning

Always set a fan to draw fumes away you, generally pointing it so that it is blowing the fumes in the same direction as the larger air flow in the studio. A very large fan doesn't always do the job alone, since the fumes seem to rise and find your nose. However, with an additional small fan sitting right next to where you are currently soldering, the fumes just move away.

Wearing an appropriate dust mask as illustrated by the Bohem Stained Glass Studio is the best solution.

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.

Heavy Metals in Glass

Some concern has been expressed about the metals used in colouring glass.  This centres around the temperatures used in fusing and whether kiln workers may be of risk from these heavy metals vaporising.

First of all, let’s get some sense of perspective. This is from Greg Rawles, an acknowledged expert on the hazards of working with glass.

Understanding Exposure:

In reality, unless you are doing:
High-volume production work that exposes you to a health hazard all day long
You are exposing yourself to high levels of a health hazard for a brief time
You are working with a very toxic material
You are not working responsibly

You are not really at risk for an unacceptable exposure when working in a glass studio  http://www.gregorieglass.com/chemicals.html

Now, let’s think about how likely it is to have heavy metals vaporise at kiln forming temperatures. How stable would glass be if the metals that colour it vaporised when we fired it? the colour would vary with the heat and number of times we fired it.

Now, let’s think about how likely it is to have heavy metals vaporise at kiln forming temperatures. How stable would glass be if the metals that colour it vaporised when we fired it? the colour would vary with the heat and number of times we fired it.

Even if the metal were to evaporate, how much is in the glass. Apparently, Bullseye uses less than 3 pounds of cadmium for a pot of glass. We can tell from the sheet numbers that a pot of glass gives at least 2000 sheets of glass, so there is ca. 0.0015 lbs or .07 grams or less of metal in a sheet of 3mm glass. There is very little there to "vaporise", so even it were able to evaporate, it is in such small quantities as to be negligible, and the exposure so low as to be of extremely low risk. There is however, no risk in protecting yourself with dust masks. Just remember that the risks from vaporised heavy metals is much less than most of the other studio practices involving glass. If you need breathing protection for metals (and you may feel it is not worth the risk) then you need to be wearing a mask all the while you are doing glass work. It is about relative risk.

For complete information, the melting and boiling points of various metals relevant to glass colouring are given below.  The vaporisation will be somewhere above the melting point and toward the boiling point.  You will be able to see the relevant temperatures and take any precautions you feel are necessary.  Remember that the metals are not used in their pure forms, but as oxides.  These may have different melting and boiling temperatures.  In general, the oxides used in colouring glass have higher melting and boiling points than the pure metal.

Antimony -for whites

Melting point: 630C

Boiling point:  1635C

Antimony Oxide

Melting point:  380-930C

Boiling point:  1425C

Cadmium 

Melting point: 321C

Boiling point:  767C

Cadmium sulphide - yellow

Melting point: 1650-1830C

Boiling point:  2838C

Chromium 

Melting point: 1907C

Boiling point:  2671C

Chromic Oxide – for emerald green

Melting point: 4415C

Boiling point:  7230C

Cobalt 

Melting point: 1495C

Boiling point:  2927C

Cobalt Oxide- blue to violet

Melting point: 1900C

Copper 

Melting point: 1084C

Boiling point:  2562

Copper Oxides - for blue, green, red

Melting point: 1232-1326C

Boiling point:  1800-2000C

Gold

Melting point: 1337C

Boiling point:  2970C

Gold Chloride - red

Melting point: 170-254C

Boiling point:  298C

Iron

Melting point: 1538C

Boiling point:  2862C

Iron Oxide – for greens and brown

Melting point: 1377-1539C

Boiling point:  3414C

Lead – for yellows

Melting point: 327C

Boiling point:  1749C

Manganese 

Melting point: 1246C

Boiling point:  2061C

Manganese Dioxide – purple and a clarifying agent

Melting point: 535-888C

Neodymium

Melting point: 1024C

Boiling point:  3074C

Nickel 

Melting point: 1455C

Boiling point:  2730C

Nickel Oxide – for violet

Melting point (II - for green): 1955C

Melting point (III - for black): 600C

Selenium

Melting point: 221C

Boiling point:  685C

Selenium Oxide – for reds

Melting point: 118-340C

Boiling point:  350C

Silver 

Melting point: 961C

Boiling point:  2162C

Sodium

Melting point:  370C

Boiling point:   882C

Sodium Nitrate – a clarifying agent

Melting point: 308C

Boiling point:  380C

Sulphur

Melting point: 115C

Boiling point:  444C

Sulphur oxide - for yellow to amber

Melting point:  17C

Boiling point:   45C

Tin 

Melting point: 231C

Boiling point:  2602C

Tin Oxides – for whites

Melting point:  1080-1630C

Boiling point:  1800-1900C

Uranium

Melting point: 1132C

Boiling point:  4131C

Uranium oxide – for fluorescent yellow, green

Melting point:  1150-2765C

Boiling point:  1300C