Development of the carbon dioxide process of moulding and core making in 1947 marked the advent of an epoch-making era in foundry practice. Sodium silicate, also known as waterglass, is employed as a binder. The amount of liquid silicate binder used for cores and moulds varies from 2.5 to 4 %, depending on the type of aggregate, grain fineness, and degree of contaminants. This moulding aggregate can be rapidly hardened by passing the carbon dioxide gas through the mould or corebox to precipitate silica. It takes only a few seconds. The process of the gas hardening can be accomplished either within the box or after stripping. The carbon dioxide can pass directly into the box through a venting system designed to achieve uniform distribution and avoid dead zones. The hardening treatment can be applied for small cores and moulds as a step in a core-blowing or core-shooting sequence. Separate hardening after stripping requires the addition of cereals or clay to the binding system to get the minimal green strength needed. When applying CO2 into the moulding aggregate, its strength increases rapidly up to a certain maximum, and then decreases – the strength of bond becomes impaired by overgassing. With regard to the strength, practical CO2 dosing should not reach the maximum strength point. The excess uncured silicate binder in the air freely dehydrates by staying in the air, and the strength continues increasing with ageing. The sodium silicate binders are not thermally degraded, the aggregate therefore retains high strength after the casting, and so additives may be used to improve shakeout or collapsibility. Like cereals, coal powder and wood flour, dextrin also improves collapsibility. Coreboxes and patterns may be made of wood, metal, or plastics, and should be washed regularly to prevent the sticking problems caused by a build-up of sodium silicate.