Mokumé gane / Forging Copper
You can form copper pipe into a solid ingot simply by melting and pouring into a small homemade mould.
However, Joe-Caswell is right, if you just want solid copper, it is so much easier to buy a hunk than to fool with copper pipe.
Alan- especially considering your interest in the katana, some research into mokumé gane may be interesting for you as a traditional guard material.
It is essentially a Damascus steel - like material made up of non-ferrous materials, usually copper-based alloys.
The info given was gained from my interest in mokumé gane
In making up the traditional Japanese alloys of Shakudo and Shibuichi, they are both copper based. Some practice in melting pure copper can be useful as a precursor to making the other alloys
Your idea is actually not as far off as you might think, copper tubing as used in plumbing supply pipe is alloy
# ETP 110
Electrolytic Tough Pitch # 110.
It is the recommended alloy for mokumé gane.
Get Steve Midgett’s video & book– (I got it from my college through a loan between colleges)
http://www.mokume.com/bookvid3.html
He shows how to make mokumé as well as prep alloys.
“The Complete Metalsmith” by Tim McCreight is also a good source of general metal working info for jeweler/cutler.
Now the how to ... this is quick & dirty so I recommend the books and videos but that said...
Clean the copper pipe inside & out to reduce scale formation. (I split the pipe with a hacksaw, pound flat and sand inside & outside with abrasive cloth.
Cut up the cleaned copper pipe with tin snips into little bits...
Create a charcoal block from hardwood. Half burn some wood.
Carve a depression in the charcoal to melt into (and a grooved spout to pour with. -Optional)
Make this thicker than you think; the charcoal will burn off as you use it.
Using a REDUCING flame on your Oxy acetylene torch, melt little bits of copper in the depression keeping the torch on it the whole time.
The reducing flame acts as a barrier and protects against oxidation (oxidation = brittleness)
Add a bit of flux such as borax. If pipe is clean, charcoal block & reducing flame mean flux may not be needed.
After it is all melted, the surface shows shiny bright, if not- flux it.
Reduce your oxygen to get a cooler flame and allow the melted copper to solidify.
(keeping flame covering it until solid and cool)
You have the option of carving the depression in the block to semi shape,
or, pouring into a mould you have made of plaster, steel, sand, soft firebrick...
A simple ingot mould can be made from two mild steel plates ¼" thick, a bit of square rod bent into a U shape and a small c clamp.
The thickness of the rod determines the thickness of the ingot.
Flare out the top of the U – provides a sprue and improves density...
Clean the steel,
Coat all pieces contacting the copper with carbon by flaming the steel with a dirty acetylene flame.
-this acts as a release agent to prevent sticking.
Put the U between the plates and clamp together.
Preheat the mould in a toaster oven at 350F to ensure it is dry- improves density, reduces voids
Pour into the mould, keeping the reducing flame covering the copper at all times.
After the cast, the ingot will be a bit porous and will benefit from a light cold forging.
When planning your ingot, keep in mind 1” x 1” x ¼” solid lump will weigh about 1.4 oz (40 grams)
When forging copper,
Annealing and forging are opposite to steel.
Heating to red then slow air cooling hardens, not softens,
Cold forging causes work hardening and requires annealing on reductions of approx 1/3.
To anneal- heat to a red heat and quench in water.
Copper alloys are considered“hot short” - meaning it is brittle at red heat.
Forging to shape is done cold, or at a black heat (colder then red heat-hard to judge-work in the dark)
This info all applies to silver as well.
Steven Penner
I'm going to presume you're joking and aren't, say ... a thief. 
