The glass master is coated with the nickel vapour up to a typical thickness of around 400 nm. The finished glass masters are inspected for stains, pinholes or incomplete coverage of the nickel coating and passed to the next step in the mastering process. Electroforming occurs in "Matrix", the name used for the electroforming process area in many plants; it is also a class 100 (ISO 5) or better clean room. The data (music, computer data, etc.) on the metalised glass master is extremely easy to damage and must be transferred to a tougher form for use in the injection moulding equipment which actually produces the end-product optical disks. The metalised master is clamped in a conductive electrodeposition frame with the data side facing outwards and lowered into an electroforming tank. The specially prepared and controlled tank water contains a nickel salt solution (usually nickel sulfamate) at a particular concentration which may be adjusted slightly in different plants depending on the characteristics of the prior steps. The solution is carefully buffered to maintain its pH, and organic contaminants must be kept below one part in five million for good results. The bath is heated to approximately 50 °C. The glass master is rotated in the electroforming tank while a pump circulates the electroforming solution over the surface of the master. As the electroforming progresses, nickel is not electroplated onto the surface of the glass master, since that would preclude separation. Plating is rather eschewed through passivation and, initially, because the glass is not electroconductive. Instead, the metal coating on the glass disc, actually "reverse"-plates onto the nickel (not the mandrel) which is being electrodeposited by the attraction of the electrons on the cathode, which presents itself as the metal-coated glass mistress, or, premaster mandrel. Electroplating, on the other hand, would have entailed electrodeposition directly to the mandrel along with the intention of it staying adhered. That, and the more rigorous requirements of temperature control and purity of bathwater, are the main differences between the two disciplines of electrodeposition. The metal stamper first struck from the metal-coated glass is the metal master (and we shouldn't make a master from another master as that would not follow the nomenclature of the sequence of siring that is germane to electroforming) This is clearly a method opposite to normal electroplating. Another difference to electroplating is that the internal stress of the nickel must be controlled carefully, or the nickel stamper will not be flat.