I believe if it is made in a terribly wrong way resulting in a very large particle size (larger than what would be classified as a colloid), or if the person somehow created a salt of silver by the presence of other chemicals, that may be the cause of the ONE person who turned blue. The particle size should be small, the silver should be 99.99% pure, and distilled water is the right starting point. Not tap water, not sodium bicarbonate dissolved in water. Distilled water although it has low conductivity has enough conductivity to start the process or dislogding silver atoms from the electrodes, and then gradually becomes more conductive. A device that alternates polarity of the electrodes, and/or gently stirs either with a lab stirrer or aquarium bubbler, dislodges the tiniest particles of silver from the electrodes, ensuring a small particle size. Also the electrodes should be cleaned/polished after each use with a bit of Scotchbrite.
A device called a Hanna Meter can be used to measure the conductivity of the liquid.
>>8414387 Of course you can use Colloidal Silver externally in any way you can think of. It is non-irritating and non-stinging. Eyes, drops in ears, nose, gargle, spray on skin wounds, spray on bandaid, spray on your feet or in your shoes, armpits, crotch. Even those who don't want to take it internally can feel totally comfortable spraying it externally. In our experience wounds sprayed with colloidal silver (as needed) will heal at least twice compared with untreated. It is our 'go to' treatment for any kind of wound.