Options available for repairing a cracked porcelain sink depend on the size and nature of the crack and the condition of the sink, but they are generally limited to replacement and refinishing. Replacement may be the most practical option, especially for large deep cracks and for older sinks.
Repairs may be possible for minor cracks, but the work requires a professional. Some companies such as Miracle Method claim to have a unique process that can extend the life of a sink and tub by up to 15 years. Custom Ceramic Coatings also performs ceramic refinishing, but there is a long waiting list, and the customer must ship the sink to Lenzburg, Illinois.
Most experts do not recommend the do-it-yourself kits sold in hardware stores, as they seldom work and often contain strong acids that are hazardous to the environment and the homeowner.