Re: How do you make colloidall gold and platinum

A colloid consists of very small particles suspended in a solvent, 
typically water.  Usually electrical charges on the surface of the 
particles keep them from contacting each other and fusing together to form 
larger particles.  Sometimes these charges result from the chemistry of the 
particles, as is the case with silver sols.  Sometimes surfactants must be 
used to produce the desired charges on the particles.

Colloidal particles have very high surface areas.  To produce a colloid, a 
method must be used to develop a high surface area.  One method is to start 
with two chemical reactants, each in a separate liquid, which, when 
combined, form a solid precipitate.  If the two liquids are combined very 
quickly with a lot of agitation, colloidal sized particles can be produced.

Colloidal silver can be produced by striking an arc between two pieces of 
metal immersed in water.  The arc vaporizes the metal, which then condense 
into very small particles.  Laser ablation apparently can also be used to 
make some colloids.  A high powered laser focused on the surface of a solid 
causes some of the solid to vaporize.  If the ablation is performed in 
water, the vaporized solid may condense into very fine particles.

Once the fine particles are produced, the surface chemistry of the 
particles, along with the characteristics of the solvent, will determine 
the stability of the colloidal suspension.  Unless the surface chemistry is 
just right, the particles will flocculate together and fall out of 
suspension.  Unfortunatly, the area of surface chemistry is quite complex. 
 If you want to make a gold or platinum colloidal suspension, you might 
start using the same arc method used for producing silver.  If that is not 
successful, you have entered into that area of chemistry called research.  
I'm sorry that I can't be more helpful, but your request is asking for 
something that might take months or years to develop.