The Underboughs Hold Campaigns
Arcane Magic will use the rules presented in the Darksun Campaign Setting as Preserving and Defiling. Unless otherwise noted, all Player Characters are assumed to be using Preserving magic, and no additional rules are required. It is enough to understand that the act of casting arcane magic is an arduous and taxing task, and special care must be employed in order to control it in order to achieve the desired and expected results. This caution is assumed to be inherent in the arcane magic rules as presented.
The true nature of Arcane magic becomes appearant when a caster does not use this extra care and caution, either wantonly or through necessity. This practice literally leeches the life forces from the world around the caster, souring and defiling the area around him. Plants wither, animals and people suffer crippling pain, and the very earth beneath his feet is turned to ash, all in order to fuel the intesity of the casting.
This act is known as Defiling, and it is easier to master, and far more intoxicating than the structured and disciplined art of Preserving. It is due in large part to the act of Defiling, that much of the mortal world reviles its use, and will hunt those who harness arcane power and destroy them. In fact, in many realms, spellcasting itself is illegal, and those who employ its methods often must conceal its use in some fashion.
In game terms, as long as you use an arcane power without using Arcane Defiling, you can disguise the magic as another type of power source, such as Primal or Divine. In certain circumstances, a successful Bluff check might be called for when it is performed in the presence of enemies familiar with Primal, Divine, or Arcane power sources. If a spellcaster is Defiling, there is no chance of disguising the magic because of the highly visible and tangible effect it has upon the environment.