A cast resin is prepared by mixing a phenol-formaldehyde condensation product which is liquid at room temperature with an acid and with furfural, the mixture being then cast in a mould. Preferably part of the furfural is mixed with the phenol formaldehyde condensation product and the mixture of the remainder of the furfurol and the acid added. Part of the furfural may be replaced by ethylene glycol. In the examples: (1) a phenol-formaldehyde condensation product which is liquid at room temperatures is prepared by heating to about 70 DEG C. 1 mol. of phenol with 2.3 mols. of paraformaldehyde and 1/300 mols. of sodium hydroxide, allowing the temperature to rise to 135 DEG C. and cooling the mixture. Furfurol and hydrochloric acid are incorporated and the product cast in a suitable mould in the usual way; (2) example (1) was repeated with part of the furfurol replaced by ethylene glycol and (3) the process of example (2) was carried out under vacuum.
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