glasses typically the dilute solutions contain from 3 0 to 9 0 percent by weight solids based on sio 2 typically from 5 0 to 7 2 percent by weight and preferably from 6 0 to 6 8 percent by weight representative commercial preparations are outlined in u s pat nos 3 582 502 and 2 244 335 while the ratio by weight of the alkali metal silicate to acid can vary typically the ratio is at least 63 1 the silicic acid or poly silicic acid is slowly and continuously added to the composition with stirring until from about one half to about three quarters of the silicic acid or poly silicic acid has been added to the composition while maintaining the temperature of the composition below 85 degrees f typically from about 60 85 degrees f thereafter the temperature of the composition is slowly raised for example over a period of from 10 to 35 minutes to from 115 125 degrees f and held in this temperature range until the addition of the remainder of the silicic acid or poly silicic acid to the composition is complete as described in u s pat no 6 486 216 a heel based colloidal silica can be concentrated and remain stable until the.