The hammering during the sinking and the backing has made the surface of the pan stretched and soft. The grooving and the backing has also forced local tensions into the metal. Before tuning, the pan has to be hardened and the tensions have to be removed. This is done by first heating the metal and then cooling it. The whole process is called tempering.
The most important effect of the tempering is presumably to remove the local tensions. Uneven tensions in the metal of the notes would presumably make it impossible to tune the pan. As heat is applied, the molecules will be able move and the crystals of the metal will shift positions and rearrange according to the new conditions in the metal. The result will be notes with a homogeneous tension over their whole surface.
A second purpose of the tempering is to harden the surface between the notes and make it stiff, while the metal in the notes areas will be a bit softer, as it later is softened during the tuning. This will make the notes act as fairly independent resonators for the different tones.
There seems to be three different physical processes working during the tempering:
- 1. Removal of tensions - an anneal - by reconstruction of the crystal structure in the metal.
- 2. Oxidation of some of the carbon content of the metal (this is probably why it turns blue) makes the metal more tenacious.
- 3. Hardening by "freezing" the new crystal structure while cooling.
While the hardening makes the material more stiff, the oxidation seems to make it more stretchable. The amount of heating has to be balanced between these two processes. If the pan is heated too much the metal will become too relaxed - the tuners call it "slack" - and the pan will be impossible to tune. If, on the other hand, it is heated too little, it will not be hardened enough. See the theory section for a more thorough discussion of the function of the tempering.
Fig. 8.1 Tempering.
The tempering is done by putting the pan upside down on a big fire for a while and then pulling it of and cooling it, either by letting it cool by itself or by the means of putting cold water or oil in it.
On Trinidad, the pan is usually heated over a burning car tyre. The tyre will burn for about 10 minutes, but 1.5-2 minutes of the excessive heat is often enough for the tempering. If you are afraid that your neighbours or the fire brigade will be alarmed by the large amount of black smoke from the burning tyre, it also works with a large log fire, but the heating will take some more time, about 10 minutes.
Fig. 8.2 Alternative methods to support the pan over the fire are to use a stand, rocks around a pit or the left-over part of the drum.
Professional panmakers use a special stand to put the drum on while heating it over the burning tyre, see figures 8.1 and 8.2. The legs of the stand are about 15-20 cm long. The stand is often complemented by some shield against the wind to keep the fire burning steady. If you don't have a stand, resting the pan on some rocks works. To do this, dig a pit in the ground with about the same diameter as the pan and put four rocks, about 10 cm high, around it, see fig. 8.2. A third method to make a fireplace is to use the leftover part of the drum to make the fire in, see fig. 8.3. Cut the drum to a length of approximately 30-40 cm.
Light the fire and wait until it is burning with good heat. Then put the pan upside down over it, resting on the stand or the rocks. If you are using the leftover part of the drum as fireplace, you have to put some long logs across the drum to prevent the fire from getting smothered by the pan on top, see fig. 8.3. This will enable the fire to get enough oxygen.
Give the fire enough fuel to keep it burning for 10-15 minutes. Flames should appear all around the pan to make sure that it is evenly heated. If it is windy, you may have to turn the pan during the burning to prevent it from being unevenly heated.
Fig. 8.3 Burning the pan, using the left-over part of the drum as a fireplace. Photograph by Linus Torell.
The time for burning is very important, because it determines the amount of heat the pan will be exposed to. There is no exact signal for when the pan is sufficiently heated. Experienced panmakers know when the drum is burned appropriately by judging from the colour of it. The remaining paint on the inside should be crumbled and the rust should be turning from brown to blue-black. If the pan doesn't have any paint on the inside, you can see the metal first turning blue, then black and last greyish. The metal surface should be looking dull when the drum is enough heated.
A documentation of the appropriate temperature and heating time is still lacking. I have heard about many different methods and times: 10-15 minutes on a log fire or 1.5 min on a burning tyre. One author claims that it takes 35 minutes to temper properly at a temperature of 350 degrees Fahrenheit (Morin, 1988).
After about 1.5 to 2 minutes over the burning tyre or 10 to 15 minutes on the log fire, the pan is pulled out of the fire and hardened by cooling. The cooling can be done either by leaving the pan by itself in the air or by pouring cold water or oil on the surface to temper and cleanse it further. The tempering put in by self-cooling of the pan in the air is often judged to be enough, but the cold liquid will make the metal in the pan even harder. The more the pan is tempered, the longer it will probably stay in tune, but the harder it will be to tune it. Nowadays, the most common tempering method seems to be by self-cooling. Drums with thin metal or drums that are judged to have been burnt too long is sometimes cooled by throwing water into them to remove the heat faster.
As the pan now is black from soot, this might be a good occasion to clean it before doing the tuning. When the pan has cooled down, put some water and soap into it and use a brush to get rid of the rust and the soot from the burned paint.