White glue or matte medium for securing ballast?

[videobruce]

15 years ago on my 1st layout, I used the typical Elmer's white glue, diluted with tap water mixture to glue down ballast (soaking the ballast with 'wet water first). As soon as the solution dried all the N scale Atlas code 80 (what I used at the time) appeared to 'tarnish' (almost a 'weathered' look). This was only where I either sprayed or using a eye dropped applied the mixture. On my 2nd layout I'm using Peco code 55 (if that matters). I don't want to have the same problem (though the affect is nice) since I'm concerned about it affecting connections between the sections of track (all flex track).

So, which is better: Elmer's white glue or, matte medium?? Also, how about the ratio for the 'glue' to water and water to isopropyl alcohol?