Lead Casting tutorial 0.2

Lead Casting

Lead is a relatively easy material to work with on a small scale. Soft and heavy by nature, you can easily bend it by hand or scratch its surface with your finger nail. When heated it produces toxic gas that can cause brain damage. It's therefore vital that you work in a well ventilated area when melting this metal. Prolonged contact with skin will result in gradual poisoning. If you intend to hold or wear it for long periods of time it must me coated with something such as clear nail varnish.

Fishing weights (sinkers) are an obvious source of Lead. Some forms of Solder can be use as a substitute. The melting point of Lead is 327.5 C / 621.5 F. This temperature is easily attained with a kitchen gas stove. Any other metal that's used must not have a substantially higher melting point. Even if you're not using Lead it's important that you observe the safety steps mentioned in this document.

One of the main problems you'll be confronted with is the presence of air bubbles in the objects that you've cast. There are several factors that can contribute to this.

1. Impurities in the metal. This is solved one of two ways.
A) You can heat the metal until it becomes a liquid and then pour it into another vessel. After this has been repeated a few times you'll notice that an Orange/whitish/brawn/silver residue has collected at the bottom of your heating/pouring vessel. Simply scrape it out after it's cooled. This method is best if you're working with small quantities (about 200g or less) and melting the lead in the same container that you're using to pour it.
B) Heat until liquefied and then continue heating until the impurities separate and rise to the surface. Simply scoop them out with a long handled metal spoon. This method is better if you're working with significantly larger amounts of metal.

If the liquid metal contains or touches any impurities when poured into the mould it is likely to bubble and spit, creating a surface texture that resembles scrambled egg.

2. Over heating the metal. Air bubbles are a greater problem if the Lead is unnecessarily hot when poured. Heat until liquefied and then pour shortly afterwards. Lead solidifies quickly when removed from its heat source. This can be a problem when casting large objects as your metal may harden before you have finished pouring. This would result in a fractured casting.

3. Dust/dirt and/or moisture on the surface of your mould. Using a fine brush or cotton bud clean the mould's surface with a small amount of turpentine/water mixture (1 part turpentine 3 parts water). Leave until bone dry.
Your mould will eventually crack if repeatedly used. Clean brakes can be repaired with strong multipurpose glue.

4. Air is sometimes trapped beneath the liquid metal as it's poured into the mould. This can be minimised by gently pouring it into a sloping channel that connects to the mould's main indentation. This problem often occurs if you're using a flat one piece mould (usually made from Plaster of Paris, dried clay or sometimes carved cuttlefish). Hollow core casting is the best method to use when working with metal.

What is Hollow Core Casting? Imagine a cube made from plaster with a hollow shape at its centre. An empty funnel and one or more ventilation tubes connect to this central space. Your casting medium (Lead) is poured into the funnel, as this happens the air is forced out through the vent tubes. After cooling, your mould is either broken or opened/split depending on its design.

It's worth remembering that a finished casting (Lead model) can be sawn, cut and filed to remove any unwanted material.

The heating/pouring vessel

I prefer to melt the lead in the same container that I use for pouring it. This is a simple and practical method if you're using small amounts of metal (200g or less). Dividing the Lead into small chunks will quicken the melting process.

Description of pouring vessel: The lead container is made from a shallow cat food can (circumference 10.7in - Depth 1.7in - Made from thin steel). One side of the can has been pinched to a sharp point (from above the can resembles a tear drop), this allows the liquid metal to be poured out easily. Its handle is made from a flat piece of "L" shaped steel (Long handle section is 10 inches in length - downward facing bent section that is bolted to can's side is 1.6 inches long - Width 0.5in - Thickness 0.1in ).
After you've finished pouring and your vessel has cooled check it for damage. Thin metal gradually becomes brittle and crumbly if repeatedly exposed to fire.

If you're working with large quantities of Lead you'll need to melt it in an old (no longer used for food) Steel or Aluminium pan. Once molten the metal would be scooped out with a ladle like tool.

Melting

Insure that your work place is well ventilated (open windows, nice draft flowing through) and uncluttered. You'll also want a supply of cold water relatively close (kitchen sink). If you burn part of you body, run cold water over the effected area for approximately 20 minutes and then seek professional medical help. Protective clothing is advisable (I usually improvise by wearing thick denim jeans and leather boots). Molten metal can/will burn through clothing and burrow into flesh. A thick leather apron would also be very useful. This is one reason I prefer using small amounts of Lead. Strong heat resistant gloves are necessary when handling hot equipment. You'll need to create a safe place to put your pouring vessel after you've stopped using it (so you don't burn your table tops or self). Don't repeatedly drop it into water as this will make it brittle.

When you're sure that your work area is safe and practical turn on and light the stove. Before you try casting anything out of Lead practice melting and pouring small amounts of it. It's difficult to give precise instructions about gas stoves as I'm unfamiliar with your equipment. On my stove I use the largest gas ring and turn it up to about 75% power. I put on my gloves and then suspend the heating/pouring vessel (containing about 100g of chopped Lead) in the peak of the blue flame. Within a couple of minutes it becomes a silver liquid. If something doesn't seem to be right I place the pouring vessel somewhere safe and turn off the gas supply. When pouring Lead it's not uncommon for some to spill/jump out of the mould. Keep yourself (mainly face and hands) at a safe distance. Try to cover your work surfaces with something that will prevent damage (burning).