[jerrry94087]

I made 1 gallon of silver water. I used clean glass jar, distilled water, silver electrodes made of ultra pure .9999 silver, 15 V power supply. It took ~3 hours, I stopped when laser ray through the water became slightly visible in darkness. At the same time water was becoming a bit yellowish, which, according to instructions from internet, is normal.

Now, after this gallon of silver water stayed for 10 days in the dark place, I noticed that water became very yellow, approximately the color of the average urine.

During the process, a lot of dark gray material formed on the electrodes, which I was wiping every 10 minutes, but some little visible pieces still dropped on the bottom.

This increasingly yellow color is worrying me. Why does this happen? What is it's chemical background? Is it normal?

[Arkcon]

Colloidal dispersions of metals in water do have strange colors, the famous example is the ruby red color of colloidal gold.  As for why the color gets stronger, I don't know -- perhaps something in your system, either the vessel or the electrodes (regardless of how pure they claim to be) or their connectors is leaching something.  You've kept it in the dark, but you need light to examine it -- maybe that's enough light for a photochemical change?

[jerrry94087]

... perhaps something in your system, either the vessel or the electrodes (regardless of how pure they claim to be) or their connectors is leaching something.

Now reading here http://johncfish.com/silver/index.htm (section "Yellow Colloidal Silver") I learn that some manufacturers of colloidal silver water purposefully achieve yellow color by adding saline solution. This gave me the idea that maybe distilled water still had some NaCl in it and this caused the color to develop. They also claim that such yellow silver water has longer shelf life.

[Borek]

Yellow/brown makes me think about silver oxide.

[ajkoer]

Fine Silver in solution may be reacting with CO2 (dissolved in the water or air contact) to form Silver carbonate (yellow).

If I am right, the suspension in the solution with time will turn even darker (tan, brown,..) per the reaction:

 Ag2CO3 --> Ag2O (a brown/black solid) + CO2

Also, Silver may be reacting with traces of sulfur, and then the Silver sulfide is reacting with CO2 forming Ag2CO3 and H2S. Any dissolved H2S may again react with the Ag, and the cycle repeats as long as you are opening the container to look (and exhaling CO2) to replenish the required CO2. In other words, you are contributing to the contamination.

[CrazyCh3m]

Take also in consideration that a colloidal solution of silver nanoparticles give a yellow colour due to the light scattering