1969 Race Dart w/ 426 Hemi- garaged for 45+ years

I used corroseal brush on.. and phosphoric acid in a bug sprayer for like inside the frame and places i couldn't brush.. then used the eastwood paint that comes with a long tube to paint inside the frame.. just something to keep in mind :) funny thing is these cars will probably never see a drop of water again so it's kind of pointless:)
So watching this video...................It is a very thin liquid when sprayed on and white. After it dries and cures it turns dark black?