Copal varies in quality, as hard, half hard, and soft, and gives best results when dissolved in properly heated vessels. Soft gums contain a small percentage of water, and if cold turpentine is added to the gum when dissolved in spike oil, precipitation is the result. Copals do not readily dissolve by cold solvents unless the gums are powdered; they may then be dissolved in spike oil, it thoroughly mixed. To prevent precipitation when thinning out, use one part of spike oil and nine parts of turpentine free from adulteration.