Possible Clues:

• That's the time it gets sound although soiled
• Goes on ahead at that time to get soiled, perhaps
• Get sound ( and soiled, perhaps) at that time
• Seems at that time it gets sound and ground
• Pottery will make it get sound at that time
• At that time 20 down gets soiled, perhaps
• Soiled, perhaps, and sound afterwards
• Although perhaps soiled, it could get sound, given time
• (Of a pot) made of fired clay
• Make the inside of clay