Well.......
my .02c.
Firstly well done on dealing with the issue and flying the aircraft.
You say it started when...."
as I was climing up between 400 and 600 AGL, the fog started, and obscured about 50% of the lower outboard portions of both windsields. I asked my mentor to get me some defog going, and he was right on it. Within a second or so, complete IMC inside the cabin, which remained for close to ten minutes with only minor improvement.
Essentially you made a sauna.
by adding heat at that point it evaporated the moisture, increased the inside air temp at a great rate and the moist air was spread all over the A/C.
maybe adding heat to the moist air was not the best solution when you were at this alt.
Sometimes when the heat is applied without the AC, it fogs up worse because your accelerating the condensation. It gets worse until the temp is equalised between the air & objects inside and the windscreen and the moisture gets reduced cause its so much warmer.
essentially what you did is turn the slowly forming dew into rapidly forming.
The dew point/fog on the outside shouldnt be so bad as long as you kept your airspeed up? I not know about a fancy ship like the EC120 but most moisture on the outside would start to collect into bigger bits would blow off I would imagine.
It wouldnt have been an issue so much if you had AC and used heat or cold becuse the AC is removing the moisture in the air especially well when its on recirculation & not fresh.
Think about rear window defoggers in a car for a sec. All it is, is some wire usually inbetween layers of laminate glass that heats up the glass on BOTH sides so that fog or dew can't form.
Large dew point spread !
Or even anti ice windows in jets (cause I have not seen one up close in a heli) it is a small section of glass that is surrounded by heat strips that keeps it very warm so the fog/dew/ice can't form.
I would say the best thing to have done with out AC would have been to land when you saw the dew forming on the inside and wipe it off.
Rainex & similar products are great on cars and bike screens but not sure how it would react with the screen in a heli.
That was a lot for .02c wasn't it.
HF