How to make a barebow weight with a potato

Posted here by permission of the author, James Cosimini, from a thread he started on Archery Talk.  James is an integral part of Brandeis University Archery

Ever wanted to mold something, but didn't have any plaster of paris, or the time or inclination to make a model, mold it in the plaster, then wait a while for the mold to dry out?
In short, I made a single use mold out of a potato, then poured molten lead into the cavity and made a weight. Did this with a good friend and teammate, (Funditor here on AT), who shoots FITA barebow in addition to olympic.

First, take a large potato. Slice off a section, and hollow out the shape of the final product (We made a U shaped kinda thing that fits the bow quite close).
Proceed slowly! Don't make a sprue (pour) hole yet. When everything is as you want it, look at see- did you screw up anywhere and make the sides too thin? Hopefully, if you did, it is in a location where everything will flow freely if you make the sprue hole there. (whew!)
Good. Now put all the parts back! Notice, I made mine closed on all sides, but you could also leave one side fully open and forget about pouring into a sprue. I used nails, but you could wire it shut or something like that. I'd avoid the Handyman's Secret Weapon (duct tape), as that has the potential to melt if hot lead gets on it.

Unfortunately, we decided to photograph the effort after the mold had been assembled, so here it is after the finished product was removed. You could probably make 2 or three weights this way, but then the mold would start to degrade (errrr....overcook....) and quality would go down.

And here it is, nailed together.

Now, assemble the following-
-Propane (or other similar) torch, and something to light it with.
-A big hunk of lead (I used a 2 pound SCUBA belt weight), or many small hunks of lead (fishing sinkers or the like).
-Something to hold the lead with while you torch it (pliars)
-Something to hold the something to hold the lead with while you torch it (hot pad)
-Someone to hold the something to hold the something to hold the lead with while you torch it (your co-conspirator)
-A crucible of some sort. (True story- my co-conspirator was forced to eat tuna fish salad as we were assembling the materials). Crimp a corner to make pouring easier in the future.
-Water. Lots of water.
-Long sleeves and gloves (in retrospect, we should have done this)
-Cardboard or a similar work surface to pour onto.
-A sense of daring and adventure

Torch that thing! Make sure to drip some lead down so that it coats the bottom of the can (err... crucible), which will allow for much better heat conduction in a minute.

Once there is a layer of molten lead on the bottom of the can (to transfer up the heat from the steel crucible), you can place the rest of the lead inside the crucible, and heat from the bottom. Trust me, this step is necessary (well, unless you like burning excess fuel...), unless perhaps you used small shot (shotgun pellets) or the like, that already has a high surface area to conduct heat from the bottom.
Try to explain what you're doing to the neighbors when they come outside and start their little hibachi grill next to you. Assure them that yes, you know what you're doing.
While holding the apparatus with one hand, remove your phone from your back pocket and answer it. Wonder why your mother isn't surprised when you tell her that you're playing with molten lead, a torch, and a potato.

I'm melllllttttiiiiinnnnnggggggggg! Do this outside, away from stuff that can burn. Keep water on hand (we had it, just didn't take pictures of it.) Take a stick and scoop off all that nasty slag on top- it detracts from a high quality pour.

Remember that piece of cardboard up in that top picture that you're supposed to pour on? Yeah, to get out of the wind we moved down onto the steps into the lee of the wind, and didn't move the cardboard with us. Whoops. Removing the big chunks of lead from the sidewalk wasn't the problem (they come right up), the issue is picking up all the little tiny splatters the size of a pinhead.
Anyways! Pour that good hot molten lead into your potato mold! Watch out for splatters and steam- this is after all pouring molten metal into a moist environment. This is why I'm now recommending long sleeves and gloves.

Pour some water over it after a couple minutes, just to make sure it's cool. Lead inside the potato actually cools pretty quick, due to the high heat capacity and high heat of vaporization of water. Lead not touching anything wet (like, on the sidewalk...) takes *significantly* longer, so give it all a thorough dousing with water.
Then, open it up and pull out your product in the rough! I think initially my lead may have been too hot, giving the poor finish quality directly beneath the sprue.

Cut off the sprue, file it down a touch, make it pretty. But not too pretty, or people won't believe you made it with a potato!

Drill out a hole to bolt it on to your riser. AHHHHHHHHHH MY HAND! (Editor's note: staged photo- no hands were harmed in the making of this photo essay)

Semi-finished product- Good enough to go to practice with and try out, considering by now we were two hours late.

Bolt it on! It fits well, nice and close (especially considering I free cut the mold!), and he shot quite well with it tonight. He'll clean it up later with a finer file, and perhaps some paint.

Brandeis Archer Shira M T Rosenblum observes as Michael Collins tests his newly weighted barebow: