The crafting and burning usually removes most of the paint in the bottom of the drum. The bare steel will soon start to rust if it is exposed to the air moisture. During the first year, the only problem will be that the pan looks ugly. But later the sound will be affected by the rust and in the long run the rust will go through the metal and ruin the pan. Therefore, if you want the pan to last it needs to be preserved in some way.
Nowadays, the most common method to protect the pan is to electroplate it with a layer of a non-corrosive metal as zinc or chromium. This is an industrial process and basins with electrolytic solution are needed. It is usually done only on small instruments such as tenors and seconds. Larger pans such as bases are usually painted on the side and the playing surface is covered with a thin layer of fat, such as car wax. The best is to combine both methods, first chroming, then a putting on a thin layer of wax to protect the surface from moisture and make it shiny.
Removing the paint
To get the shielding layer of zinc or chromium to stick to the drum the remainder of the original paint has to be removed. This is preferably done with calcinated soda. If the paint is of a hardened lacquer type, the soda won't affect it - it has to be removed by grinding. The paint can also be removed by sand blasting, but this makes the surface dull, and is not recommended if you are going to chrome the drum later. If the pan is to be chromed, the factory will probably put it in a bath of acid to remove the last paint and fat, but usually the factories want most of the paint removed to avoid messing up their acid baths.
If the pan is going to be painted on the sides instead of chromed, it is sufficient to grind the original paint enough to roughen the surface to get the new paint to stick to it.
Chromium or zinc covering
Chroming or zinc covering is usually done by factories, using electrolytic processes. On Trinidad, chroming factories are used to the panmakers needs and know how to handle pans. Therefore, the chroming is cheap and straightforward. In other countries, it may be hard to find a factory with an electrolytic basin that is big enough to handle a pan. The shape of the drum also causes trouble, since the electrical currents in the electrolytic bath will not reach into the inner parts of the drum. To insure an even coating of chrome or zinc, one or several "support anodes" (extra places to send current into the bath) have to be inserted into the drum, which makes the process even more complicated and costly.
The coating has to have two important properties: It has to be thin, and it has to be soft, i.e., it has to stick to the surface when the note is buckled during the tuning. If the layer is too thick it will affect the tone and damp it. The maximum thickness is still unknown to me, but a layer less than 0.1 mm in thickness should not affect the tone. If the layer is too hard, it will burst and start to fall off when the tuner is doing the final tuning. Some types of zinc or chrome layers are designed to give a hard, shiny surface. These are not suitable for pans.
The electrolytic process will put a thin layer of chromium or zinc all over the drum, except for the innermost angle between the outer notes and the skirt. The electrical field of the electrodes used in the electrolytic basin will not reach down to this narrow place. Therefore this part has to be shielded against rust in some other way. The best method is to cover it with a thin layer of paint as soon as it comes back from the chroming. If this not is done right after the finishing, you have to start by applying rust-eater to remove the rust.
When painting the playing surface, it is important not to use a paint that not is too thick, because this will damp the harmonics of the note and make the sound dull. Another undesirable effect of thick paint is that it makes the pans (especially the basses) rattle when it dries in the uppermost angle between the notes and the skirt. The best is to use spray-paint or to make the paint thinner before applying it. For chromed pans, it is often enough to paint it 5-10 cm up on the playing surface and the skirt, see fig. 12.1. If spray-paint is used, it may be applied to the whole playing surface of basses and other big pans that have not been protected by chroming.
Fig. 12.1 Painting the pan to protect it from rusting after chroming. Cross-section of drum.