sentences:  The pattern needs to incorporate suitable allowances for shrinkage; these are called "contraction allowances," and their exact values depend on the alloy being cast and the exact sand casting method being used.Some alloys will have overall linear shrinkage of up to 2.5%, whereas other alloys may actually experience no shrinkage or a slight "positive" shrinkage or increase in size in the casting process (type metal and certain cast irons).The shrinkage amount is also dependent on the sand casting process employed, for example clay-bonded sand, chemical bonded sands, or other bonding materials used within the sand.