js55,
excuse me for the delayed answer; I've been out of town for a few days.
Dave is right at saying that when moisture combines with the coating material it'll need a higher temperature to get rid of. This is the case of basic (or low hydrogen) electrodes whose coating is made predominantly of calcium oxyde (chemical formula CaO), usually called "lime". When it absorbs moisture, i.e., water vapor, the calcium oxyde combines with water to give calcium hydroxide, usually called " hydrated lime", which is a new chemical substance. The chemical reaction is CaO + H2O ----> Ca (OH)2. In order to split it again into lime and water vapor a higher temperature is required, as Dave correctly says.
The case is different when the coating material doesn't react chemically with water, as is the case of cellulosic and rutilic coatings. They'll absorb moisture but won't react with it. In this case, the absorption or release of moisture will depend, as physical chemistry says, on the vapor pressure of the moisture within the coating and the partial vapor pressure of moisture in the atmosphere. Both of them depend on temperature and the latter depends also, as Dave correctly points out, on the altitude above sea level. If the vapor pressure of moisture within the coating is higher than the partial pressure of moisture in the atmosphere, then the moisture within the coating will be released. If the partial vapor pressure of moisture in the atmosphere is higher than the vapor pressure of moisture within the coating, then the coating will absorb moisture.
In order to make those calculations you must know the altitude of your oven above sea level, the atmospheric pressure at that altitude, the moisture vapor pressure and the relative humidity (% humidity) in the environment in that particular day. For that, you should have at hand the psychrometric chart, steam/water tables and a table showing the normal atmospheric pressure at different altitudes, which is commonly found on compressed air manuals. Of course, you should have some basic knowledge of physical chemistry.
Knowing that water boils at 212 F at sea level, (i.e., at 212 F all water has evaporated), instead of making calculations it's easier to state a temperature higher than that (250 F in this case) to bake the electrodes and make sure that there will be no moisture into the coating (or there will be very little).
Giovanni S. Crisi