Introduction: Lard Lamp - a Solid Fat Burner Made by Lost Wax Casting

Here's how to make a very simple little fat-burning lamp that is specially designed to be used with fuels that are solid at normal room temperatures, such as the leftover fats from cooking bacon, sausages, duck, lamb, etc.
The reason it is able to do this is that surrounding the wick, there are protrusions in the shape of petals - these capture some of the heat from the flame, which is then conducted down through the body of the lamp and dispersed through the feet, heating the fat reservoir and keeping it liquid and able to flow up the wick.

It's made by Lost Wax Casting using everyday materials - this method is quite easy and can be used to make a wide range of other small metal objects.

In brief, Lost Wax Casting consists of:
  • Making a wax model of the object you want
  • Encasing the wax model in something heatproof such as clay or plaster
  • Melting out the wax
  • Pouring molten metal into the space left by the wax
  • Removing the mould material and tidying up the finished object

Step 1: Step1: Gather the Necessary Materials

OK, so we'll need some pliable wax.  You might be able to make this yourself by melting candles and blending it with vegetable oil or vaseline, but the easy option is just to eat some cheese - the red wax protecting the rind of Edam cheese (and some other varieties) is perfect - pliable and malleable like modelling clay if warmed in the hand a little.

You'll need something to make the mould.  I used decorating filler.  Patching plaster or plaster of Paris will all work quite well.  Potter's clay can be used instead, but must be pressed into place around the wax model, which isn't easy for delicate work.

You'll need some metal for casting.  You can buy pewter or white casting metal in ingot form at good craft stores and online, but I just bought an old (but not antique) dented petwer tankard from a charity shop - it was really cheap.

And you'll need something to melt the metal in - an old food can is good - as wide and flat as you can find.

Step 2: Step 2: Make the Wax Form

Start the wax form by warming a small ball of wax in your hand, pushing a pencil through it, then rolling it between your palms so that it forms an elongated cylinder around the pencil.

Use a sharp knife to trim the ends neatly, then cut slits lengthwise at each end towards the middle (but not meeting in the middle)  If you want your lard lamp to have four petals and four legs, cut four slits at equal spacing around the wax cylinder.

Remove the cylinder from the pencil and splay out the four segments ar either end - the ones which will form the feet need little done to them.  Shape the top ones into petals (or something else, if you like)

Add a small ring of wax where the wick will emerge - and any other small details you fancy.  The petals can be engraved carefully with a toothpick at this point, if you like.

If at any point, the wax becomes too soft to hold its shape properly (which can happen if you're handling it a lot), just put it in the fridge for a while.

Finish the wax form by fixing four small cones of wax to the bottom of the feet - these will form channels into which the metal will eventually be poured.

Step 3: Step 3: Prepare and Set the Mould

Select a container in which to make the plaster mould - this should be larger than the wax form in every direction.  I used the bottom of a plastic bottle.

Stand the moulding container in boiling water, then place the wax form into it - the bottom of the wax cones should melt and stick where they touch the warmed plastic, then remove it from the hot water and leave to cool and set. (it's actually not a bad idea to put the whole thing in the fridge at this point, to toughen up the wax ready for the next step.

Ignore the instructions on the decorating filler or patching plaster and mix up a batch using sufficient water to bring it to a thick, but pourable consistency.

Pour the plaster over the wax form to cover it by at least an inch above the highest point.

Agitate the mixture carefully by plunging a bamboo skewer up and down in the corners (or any place that you know is well away from the actual wax object hidden inside) - doing this should help any small air bubbles to rise - meaning the plaster should hug the wax form more perfectly.

Step 4: Step 4: Time Passes...

Leave the plaster to set for a couple of days - it will take longer than the drying time on the pack for two reasons: because we used more water than the pack dictated, but also, because it's a big, solid block of material

It will dry eventually though - and cutting away the plastic container after a couple of days, then leaving it in a warm, airy place will help to dry it all the quicker.

Give it at least a week drying before continuing to the next step.

Step 5: Step 5: Melt Out the Wax

Place the plaster mould upside down on the bars of your oven.  Try to align the holes underneath so that they are not directly above the bars of the shelf.

Put a foil-lined metal tray on the shelf underneath.

Turn the oven on to 100C and leave it for half an hour, then increase the temperature to 200C and leave it another half hour.

You may find that the wax melts and drips out, or you might not see any at all - in some cases, the wax melts and runs out - other times, it melts and soaks into the plaster - either way is OK.

While you're heating the mould, you can start preparing the metal for melting (step 6) - because it's best for the mould to still be hot from the oven when you cast the pewter (reducing the difference in temperature between mould and metal should allow for more even cooling and setting, as well as reducing the risk of cracking)

Step 6: Step 6: Metalwork!

If you're recycling a pewter tankard, cut it into little pieces with tin snips and place it in the metal can for melting.  Do this before or during the previous step (melting out the wax), as it's best to pour the metal when the mould is still hot.

Melt the pewter over a gas flame - I used a small butane camping stove, because I wanted to do this all outdoors (actually, in my greenhouse) - only really because of fumes from the paint and other materials on the outside of the can.

When you're reasonably confident that all of the wax has gone from the mould in the oven (after an hour of cooking, it should be) - carefully lift it out, using oven gloves or thick cloth.

Turn the mould hole-side up and put it in a dish to make it easier to handle.

When the pewter is fully melted, use pliers or tongs to carefully pick up the can and pour the metal into one of the holes in the plaster cast.  DO NOT STAND OVER THE MOULD in case it spurts or spits.  Try to work at arm's length for extra safety and wear long sleeves and thick gloves.  You shouldn't need any of this,, but better safe than sorry.

If all goes well, you should see molten metal rise up in the other three vent holes.  Steam might bubble out a bit.  Tap the mould sharply with the pliers, while the metal is still liquid, to help any air bubbles come out.

Make sure everything is safe and secure, and all hot things are left on suitably heatproof surfaces and the gas is turned off, then leave everything alone for an hour.  Keep kids, pets, etc safely out of the way of the cooling materials.

Step 7: Step 7: Remove and Finish the Casting

Break the mould apart with a screwdriver or chisel.  Go carefully, so as not to scratch the metal casting.

The casting will have extra pieces of metal attached from the pouring channels (these are called sprues) - they can be cut off with a small hacksaw, and any remaining protrusions smoothed away with a file and wet/dry abrasive paper..

Step 8: Step 8: Use Your Lard Lamp

Cut a piece of cotton rag and thread it through the lamp to act as a wick.

Place the lamp and wick in a shallow heatproof dish.

Melt the lard or fat and pour it into the dish, up to a level below the base of the petals.

Allow to cool and set.

Light the wick.  It will burn slowly at first, but the heat from the flame will soon start melting the fat reservoir and it will continue to give light for several hours.

Do not leave the lard lamp burning unattended.  Do not use it where it may be knocked over.

More discussion of this project, as well as details ofother objects made using this simple lost wax method may be found on my website.