Weathering red tank armor

 

Start by sponging on some areas where the paint fell off. 

On lighter red (e.g. Blood Angels Red), start with a 2:1 mix of Reaper Fresh Blood and Black. 

Darker red (e.g. Flesh Tearers Red) takes better to a 1:1 mix.

Sponge pure Fresh Blood, trying to keep it smaller, on the inside of the previous patches.

Finally, small sponges or brush tips of Chainmail Silver in the middle of each red spot.