Gold that was dissolved in solution, and has begun the precipitation process, where gold ions begin to gain electrons and form atoms of gold metal particles which combine in solution to form particles of clusters of these invisible gold atoms, as these small gold atoms move in solution these gold atoms crash into each other, or collide they combine and coagulate into each larger particles, which grow in size, clusters of atoms clash to form larger particles,as these particle's grow towards forming larger particles and then crystals of gold large enough to be visible in solution these larger particles of gold are then pulled to the bottom of the vessel by gravity.
These gold atoms being neutral (no static charge are free to randomly crash into each other and combine and grow to form a precipitate of gold metal crystals.
colloidal gold is these gold particles which have stopped growing in solution, their growth stunted in the process, the invisible gold atom particles are neutral (no charge) but surrounding Ions in solution can hitch a ride onto the outer shell of these growing clusters, the outer shell of the gold cluster particle can then become electrostatically charged, as these ions that attach themselves can be either negative or positively charged Ions, this gives an electrostatic charge to the growing gold clusters, now with all of these invisible gold clusters being charged of the same polarity (by the ions attached to their outer shell), these gold clusters of atoms stop growing is size, they repel each other as like charges repel, for them to grow and precipitate they must be able to come into contact with each other, this being impossible now, as they have become electrostatically charged they cannot do this they push each other away, this also keeps them in solution and in movement so they will never settle.
The gold is reduced (full atoms of gold particle clusters of atoms) so we cannot test for them with our stannous chloride.
We cannot reduce them with the cementing process of using another metal like copper (they already have all their electrons and need none from copper).
we cannot see the colloids the particles are so small they are invisible, but we may be able to see a color.
The Tyndall effect of light is where a light shine through a solution and when colloids are in the solution the small gold particles reflect the light on the side, the color of the reflected light has a direct proportion to the size of the gold colloidal particles in solution, this color may be red, blue or violet, one test for a colloid is to shine a light beam through solution and view from the side. this reflected light the Tyndall effect is proof of colloidal particles.
Gold colloids are so small they will pass through most filters even a ceramic filters, so we cannot filter them out of solution.
The stannous chloride test where we purposely reduce gold forming a colloidal gold solution with colloids of gold of a certain size, so that we can see this Tyndall effect of the purple colored solution, to indicate gold was previously in solution (but now metal floating in a solution of colloidal gold giving a purple reflection of light).
Dirt, oils, organics, tin, solutions loaded with base metal ions,and other factors can promote the formation of colloidal gold, and can cause a refiner lose a tremendous amount of his gold if he is not careful, and learns to recover and refine the gold properly.
These colloids of gold can sometimes be broken (hard to do but can sometimes be done).
High heat which can also concentrate solution (bringing particles closer together) and moving particle faster in solution, giving them more chance to come into contact together, the heat also can help to increase acidity, can help to break the colloid, and help these particles to lose their static charge and come together as larger particles to form crystals of gold that will precipitate.
Changing PH can also help to break a colloid, strong acid (Heat can also help here).
Adding an ionic salt (electrolytes) of opposite polarity of colloids is one way to break a colloid (but here you would have to know the polarity of the gold colloid and you would also be introducing more salts to contaminate your solution (not something I would recommend in recovery or refining), we could make the situation worse if we added the wrong ionic salt to solution.
Electrolysis of a solution, where we create an electric field and push the colloid to one electrode or the other, depending on polarity of the colloid, which is actually the polarity of those attached ions on the outer shell of those colloidal gold particles, so here we can force the gold to the anode or the cathode depending on the ionic charge of the colloidal gold which can be either positive or negative depending on conditions that formed the colloidal situation (and the particles may have a better chance of collision)...
Then we can also break the colloid by evaporation under heat, crystallizing the powders, incineration of, or roasting them, to burn off organics which could have caused the problem, or oxidize and wash tin which could have also be the source of trouble, and caused the problem, or dissolve and remove some of the the base metal contaminates, before we put the gold back into solution in a much cleaner situation to avoid this problem again...
We can see where incineration to remove organics, keeping tin and certain metals out of solution with gold in solution, and removing base metals before dissolving gold, and other techniques we have been taught become very important, and helpful to prevent from forming colloidal gold. Or how these precautions can keep us from tossing out our gold with those baby gold colloids in that dirty old bath water.
![CAM00137[1].jpg](https://cdn.imagearchive.com/goldrefiningforum/data/attachments/16/16330-b84ad7cd528e791ff006da502f0d12b7.jpg)
