Pictured is a head cover off a 20 year old Johnson outboard engine. This piece has significant corrosion and is something of an experiment.
The first view is the underside which has has salt water running through it. There is some furry corrosion left and some dark patches.
To start with the furry white corrosion is fairly easy to blast off. More telling is the dark patches, this is is serious salt corrosion. In places it is deep and I am told I could blow holes in it ! So this piece is really past it. However a 10 minute blast can get us to the point of being able to see into the internal water galleries rather than making a guess.