this is my technique for making colloidal gold out of AuCl made with HCl and H2O2...it is a little less forgiving than Kephra's technique using known concentrations and quantities of NaCO3, AuCL and maltrodextrin.
1L water at room temp, add AuCl and maltrodextrin in normal amounts
microwave to about 160 F,, stir and add NaCo3 until you get a purplish color change at the top of the vortex in hot water, gold, maltodextrin solution...add a little more NaCO3 and return to microwave for about a minute...should be pretty ruby red and good to go.
this order of steps gives reliable results for me, took me a little experimenting to get consistently good results using the home made AuCl. I had some purple batches and some batches that never formed colloids