Choice of electrodes considering type of coating

The coating of electrodes plays a critical role in the process of welding. After the nature of covering the electrodes can be:
Acid coated electrodes (A). They have combined iron oxides, iron silicates, SiO2, manganese oxide. Shell is thick and melts easily in the form of fine droplets. Slag is lush and fluid, solidifies with delay and it can be removed easily. 
It is welded  AC/DC, with short or medium arc. The welding cord resulted is smooth, with a smooth transition to the metal base.

Basic coated electrodes (B). They have a thick skin containing basic character components: calcium carbonate (limestone, marble, chalk, calcite, etc.)all together with calcium chloride and ferro-alloys.
Slag formed is compact and easily rises above the molten metal, and after solidification has a shiny appearance. Solidification range of basic slag is reduced (20 ... 25 °), after freezing slag in the gap is porous and difficult to remove. The Basic welding electrodes are using DC,reverse polarity, all the while maintaining an arc welding electrode as short and inclined in the direction of welding at 75 ... 80o. It can weld in all positions. There are Basic electrodes for welding, in alternating current.
Coated titanic electrodes , symbolized by (R) - Rutile, or (T) - titanic. They have medium thick skin, the last could be weld in vertical positions and over head. Shell that contains titanium minerals: rutile (TiO2) or FeTiO3.
Electrodes symbolized by R contain a larger amount of rutile. Slag of these electrodes is dense and viscous, if coating is Rutile.Electrodes (T) have a more fluid slag and less dense. Slag solidification range is quite small, about 30oC and after freezing slag is removed easily and, in the gap, it is porous.Favorably welded in all positions, especially upright dragged, at high speed work.

Cellulosic coated electrodes, symbolized (C). Shell contains large amounts of combustible organic substances, which decompose during welding and produce large amounts of protective gas, which provide protection welding bath.
Slag produced in small quantities, remove easily.
Arc easy to maintain. Drops losses are larger  that other types of electrodes and welding area has nice appearance.