Do no use leather collars for bathing, swimming and going outside in heavy rain. If a collar is got wet, take a dry cloth, wipe it and leave to dry at room temperature.
Direct sunlight is harmful for colored leather dog collars because they may change color.
Oil the collar from time to time with leather care products and it will stay soft, flexible and will be in use for a longer time.
Hold the collar in a special ventilated bag of natural material to keep it from excessive dust, dryness and humidity.