A dental mould consists of a highly refractory material such as silica, alumina &c., and a binder of silica gel.  In making the mould the silica gel is generated in situ by admixing hydrolyzable organic silicates with the refractory material and initiating aggregation of colloidal silica particles as by admixing with the ester a small amount of acid.  The initial setting may be accelerated by heating e.g. to 110 to 115 DEG  C. or by adding a small amount of an accelerator, e.g. an alkaline material, preferably magnesium oxide. In an example 8 vols. of tetra-ethyl silicate are mixed with 1 vol. of water and a few drops of hydrochloric or sulphuric acid, the mixing being aided by the addition of 1--2 vols. of ethyl alcohol or acetone.  The mixture is then stirred on a water bath for about 1--2 hours; 1 part of the binder being then mixed with 2 parts of silica (ground quartz).  To accelerate setting magnesium oxide may be mixed with the silica in the proportion of 1 : 1000 or ammonium hydroxide with the binder in the same proportions.  The highly refractory nature of the composition allows its use in soldering or welding processes or for the casting of high fusing materials particularly of porcelain.  The surface of a completed mould may be hardened by painting it with or immersing it in the liquid binder.ALSO:A dental mould consists of a highly refractory material such as silica, alumina &c. and a binder of silica gel.  In making the mould the silica gel is generated in situ by admixing hydrolyzable organic silicates with the refractory material and initiating aggregation of colloidal silica particles as by admixing with the ester a small amount of acid.  The initial setting may be accelerated by heating, e.g. to 110 to 115 DEG  C. or by adding a small amount of an accelerator, e.g. an alkaline material, preferably magnesium oxide. In an example 8 vols. of tetramethyl silicate are mixed with 1 vol. of water and a few drops of hydrochloric or sulphuric acid, the mixing being aided by the addition of 1-2 vols. of ethyl alcohol or acetone.  The mixture is then stirred on a water bath for about 1-2 hours; 1 part of the binder being then mixed with 2 parts of silica (ground quartz).  To accelerate setting magnesium oxide may be mixed with the silica in the proportion of 1 : 1000 or ammonium hydroxide with the binder in the same proportions.  The highly refractory nature of the composition allows its use in soldering or welding processes or for the casting of high fusing materials, particularly of porcelain.  The surface of a completed mould may be hardened by painting it with or immersing in the liquid binder when making a mould from the composition by contact with a reverse model made of a flexible gelatinous material, the hydrolysis of the binder of the composition is expedited by the water in the gelatinous model.ALSO:A dental mould consists of a highly refractory material such as silica, alumina &c., and a binder of silica gel.  In making the mould the silica gel is preferably generated in situ by admixing hydrolyzable organic silicates with the refractory material and initiating aggregation of colloidal silica particles as by admixing with the ester a small amount of acid.  The initial setting may be accelerated by heating, e.g. to 110 to 115 DEG  C. or by adding a small amount of an accelerator, e.g. an alkaline material, preferably magnesium oxide.  In an example 8 vols. of tetra-ethyl silicate are mixed with 1 vol. of water and a few drops of hydrochloric or sulphuric acid, the mixing being aided by the addition of 1-2 vols. of ethyl alcohol or acetone.  The mixture is then stirred on a water bath for about 1-2 hours; 1 part of the binder being then mixed with 2 parts of silica (ground quartz).  To accelerate setting magnesium oxide may be mixed with the silica in the proportion of 1 : 1000 or ammonium hydroxide with the binder in the same proportions.  The highly refractory nature of the composition allows its use in soldering or welding processes, or for the casting of high fusing materials particularly of porcelain in making artificial teeth and partial or complete dentures.  The surface of a completed mould may be hardened by painting it with or immersing in the liquid binder. When making a mould from the composition by contact with a reverse model made of a flexible gelatinous material, the hydrolysis of the binder of the composition is expedited by the water in the gelatinous model.  Such a mould is used in the manufacture of partial dentures.