Slow drying: This defect which in extreme cases can be very troublesome, may occur for various reasons. Paints applied in damp conditions or cold weather, or on surfaces where traces of dirt, oil grease or wax remain, will usually retard drying. Unsuitable thinners, such as paraffin or inferior brands of turpentine, have a similar effect on the drying of paint. Some oil paints after long storage may dry more slowly due to absorption of the driers, by certain pigment i.e. black. Alternatively, an excessive amount of driers in a paint can cause a skin to form quickly after application thus excluding air from the main body of the paint film which remains comparatively soft. Oil is then liable to sweat through , with a consequential re-softening of the paint surface, accompanied by loss of gloss. Paint applied too thickly may dry on the surface but through drying/hardening will be delayed. Remedy: To ensure correct drying it is essential to remove all traces of dirt, moisture or grease from the surface to be painted and apply the paint under good atmospheric conditions. Applying the paint too thickly should be avoided. Only the specified amount of the correct type of thinner recommended for the particular paint should be used.