Fire Blows: A Look at Blowpipes

A blow pipe is a simple devise consisting of a simple tube with a graduated interior diameter. Air is forced through the tube by means of the lungs to add extra oxygen to a flame, increasing its heat. By having the interior diameter restricted along the length of the pipe, the air pressure is increased, and the force of the air entering is focused and strengthened as it exit's the pipe to interact with the available flame provided by the use of a lamp. The flame could be produced by a simple oil lamp, an alcohol lamp, a candle or even a more modern gas fed flame. This simple technique of rapid oxygenation can produce temperatures high enough to melt small amounts of gold, alloys and solders.

What does this mean? Exactly?

(Technical stuff ahead, try to not nod off…I’ll be brief.)

While there are ways to join your various and sundry metal bits together, the most popular methods are Soldering and Fusing (or Fusion Welding).

Soldering is a process that joins two pieces of metal by using a third metal and melting it between them to form the bond. Typically, solder is used, the specific alloy depends on the two items being joined.

Fusion welding is a bonding technique for metals were two parts are heated right up to (but not past) their melting point while sitting in contact with each other. At a temperature dependent on their precise composition the surfaces of the parts start to melt and flow together. Upon cooling the two parts are firmly joined. If brought past their melting points, you wind up with a pile of molten metal cooling on your workspace, and your ears riddled with your own salty, salty language.

What do these things have in common? HEAT!

Much of the jewelers’ art depends upon heat. And not just any heat. Directed, reliable, precise heat.

While many early jewelry was made with the use of what can be described as “mini-forges”, small clay/ceramic/stone forges that used force air to create a hot spot above the forge at a chimney-like protrusion, these devices where further refined over time to smaller and smaller scale for the production of finer and finer (more fine, one might even write…blink, blink) jewelry. This culminated in what we now call the “Blowpipe”.

When a stream or jet of air is directed through a flame, fuel air mixing is enhanced and the gaseous cone of heat exiting the flame is intensely hot while at the same time controlled and directional. This is the same principle used to make forges hot, hot, HOT! But, on a much smaller scale. Jewelers engaged in lampwork have used the blowpipe since ancient times, with the blast being powered by the user's lungs. For small work, mouth-blown blowpipes had been used with candle flames or alcohol lamps. The cleaner burning the fuel used, the more controllable the process, and more predictable the outcome. Metals used in jewelry work have melting temps ranging from 1800 to 3200 degrees Fahrenheit, though 3200 is an outlier (platinum) and most of the alloys used melt in more the narrow range of 1800 to 2000. This is higher than the average brazier or camp fire will allow.

The first evidence of the use of a mouth blow pipe for alloying gold with silver and casting was in Ecuador and Peru circa 200 BC. This simple and successful technique is still used today. Starting in the 1800s, blowpipes have been powered by mechanisms, and devises of all stripe. Initially powered by bladders and bellows in the same fashion as one sees in larger forge operations, but now blowers, compressors and compressed gas cylinders are commonplace. While blowing air (atmosphere, or lung expulsions) is effective, blowing pure oxygen produces higher temperatures, and it is also practical to invert the roles of the gasses and blow fuel through air. Modern blowtorches and oxy-fuel welding and cutting torches can be considered to be modern developments of the blowpipe, the blowpipe’s spiritual grandchildren, if you will.

(Still with me…?)

During the Middle Ages, this heat was provided by the primary means of the Blowpipe.  The simplest of these tools were a tube of copper, the interior diameter of the tube graduated from its widest at the mouth-end, to the narrowest diameter at the spout end.

How does one come by such an incredible and useful tool? You make it!

I won’t go into the process involved in mining ore, smelting, refining metal, and milling sheet. This would lead to a paper that never ends. So, here we jump to a reasonable stage One:

1)      We start with copper sheet.

This THIN copper sheet (20 gauge is my suggestion for thickness for this project) will need to be annealed if not dead soft already. (Annealing is the recrystallization of metal in order to reduce stress caused by work hardening. The metal is heated; the heat (judged by color, a low cherry red glowing state) is held for a short period of time after which the metal is allowed to slowly(relatively) cool. The heat on top of your coals in the forge will work quickly for this, though you must keep an eye on the heating, too hot and the copper melts. (A modern plumbers’ torch works well for this, if you don’t have a forge. (The use of the modern torch is also safer and more convenient for the modern metal worker who has limited funds, and safe working space.)

This process removes the brittleness making the metal more malleable allowing it to be worked again without breaking or cracking. Annealing may be needed many times while working a piece.)

Once softened, you will need to cut a strip of the copper to 20mm wide by 15cm long. Taper one end into as even a point as you can make it.

2)      Roll the Strip into a tube.

Cut a straight, narrow channel into a sturdy wooden board (I tend to use Red Oak for this…very sturdy) with a rounded bottom. Lie your strip of copper into the channel. Using the cross peen end of your Goldsmiths Hammer, hammer the middle of the copper strip along its length into the round bottomed recess in the board. This will begin the process of creating a tube. (Anneal!)

Next we shall put the tapered end of the copper strip into the largest whole of your drawplate that will allow you to grasp that pointed end now protruding from the other side of the drawplate, and draw the strip through. This will bring the strip further into the shape of a tube. (ANNEAL!!) Using the drawplate, we further constrict the circumference of the tube by progressively drawing it through smaller and smaller holes in the drawplate, annealing regularly. Waxing the outer surface of the tube with a lubricant, like beeswax, will be helpful in making the draws smooth.

(A drawplate is a sheet of metal, wood, or stone with graduated holes through which wire or tubing in this case, is pulled to reduce its circumference and cause it to be toughened by work hardening. (Anneal between each drawing…))

As your sheet became strip, and the strip became tubing, the tubing became thinner, and longer via the drawing process. Be careful to use slow, evenly distributed force in each pull of your various draws, this will keep the tubing straight and the seam of the tubing straight as well.

Between each annealing, you will notice your copper is darkening. This is caused by oxidization. This can be cleaned by pickling. Pickling is a method of cleaning the surface of metals via a mildly acidic solution. Beer vinegar is the mediaeval method, though very slow due to its very low molar count. (relative acidity) A stronger solution can be made from distilled vinegar and salt. (1 tbsp. salt per 2 cups vinegar) Kept warm, (90 to 100 deg F) this solution will clean the copper surface in an hour or so. Modern packaged pickling solutions are available, and very fast and effective. All pickle works better warmer rather than colder. Once removed from the solution, rinse in clean water and dry the copper. No need to let it re-oxidize on you.

3)      Repeat this process to produce another length of tubing, with an outer circumference just thin enough to fit inside the first piece of tubing.

Do it.

4)      Solder the seams of both tubes.

Using the even heating technique of your preference, flow silver solder into the seams of each of you newly created tubes. Cut the entire pointed end from the larger tube, and the very end of the pointed end from the slammer tube. Be careful in both cases to not collapse the tubes, you need them open. Pickle and clean as before.

5)      Solder the Tubes together.

Placing the non-pointed end of the smaller tube snugly into the end of the wider, solder the two sections together. Pickle and clean. You should now have a long, graduated tube with a small pointed end.

6)      Using a burnishing pick end, slowly widen the wider of the two tube ends.

This will be the end that goes into your mouth, held by your teeth as you blow. You can further define the end using a file to cut a notch around the outer circumference to aid in giving your teeth a gripping purchase on the blowpipe.

7)      Test your new blowpipe!

Blowing into the pipe, direct the current of air across the tip of a flame from an alcohol lamp, oil lamp, or candle.

8)      Practice, Practice, Practice!

Practice will make all the difference in how useful this new tool is in your studio life. You may find at the outset that you need to build up your wind to be able to sustain a flame tip for any reasonable time. Smokers beware; this will be doubly challenging for you. 

Drawing of blowpipe in use.

Goldsmiths Hammer. 

Pair of silver flanged earrings made using copies of Bronze Age Tools for the National Museum of Ireland. 35mm. The same processes may be used to create the flanged torcs and sternum plates that were popular between 1200 and 1000 BC.

Simple ceramic oil lamp as fuel source.  

Copper blowpipe, with bent end to allow work from behind the flame.



Sources:

1) Wethered, Newton. Mediaeval Craftsmanship and the Modern Amateur: More Particularly with Reference to Metal and Enamel,

Longmans, Green, and Co., 1923.

2) Untracht. Jewelry Concepts and Technology. ,

Doubleday, 1985

3) Various. 7000 Years of Jewellery

British Museum Press, 1986