Can you tell me what is the minimum concentration of hydrofluoric acid that applied in a thin layer with a brush or something similar will etch glass quickly (until it evaporates from the glass surface)?
Hydrofluoric acid is denoted as HF. Pure HF is called hydrogen fluoride and it exists as a gas. Hydrofluoric acid is a saturated aqueous solution of HF, so it is in liquid form. HF is actually considered a relatively weak acid, which is surprising since all of the other halogens make strong acids. Even though HF is a weak acid, it still has interesting and dangerous properties. It is particularly destructive to organic tissues like skin. Initial HF burns can be very mild with little pain, but the burning can increase over time and eventually work its way down to the bone.
Probably the most interesting property about HF is its ability to etch glass. Glass is made up of silicates, and fluorine and silicon have an extraordinarily high affinity for each other. Concentrated HF is usually what is used for etching glass, and it has a concentration of about 48% (in other words, 48 g of HF per 100 g of water). More dilute concentrations could probably be used, but 48% is the standard.
I know the HF acid's risks and properties. I just want to find a good good concentration of HF acid for this specific situation. I've heard people saying even a 10% HF acid solution will immidiately etch glass, but if possible I want to get an answer from somebody working in this domain. Thanks.