Hi Adrian, hope all is well with you..
Yes, I must admit that is the best finish I have had from the Halfords 'in a can' primer. Though I did try something different this time. As with the tender I chemically blackened the whole thing as I'm petrified of paint flaking of on handrails and the edges of running boards, and then I primed with the Halfords Acrylic primer, so it now has two etchants on there.
In the past I have heated the model, and the primer up to quite warm/hot as I have been told that this will make the primer adhere and etch better, but in the past I have found that the primer can go grainy on the model, requiring a bit of remedial work with a glass fibre brush and some fine 1500 grit paper. This time I thought I would try using both at room temperature rather than warm, and it seemed to work far far better!
It was all going so well, but then I sprayed the halfords acrylic black over the top, and gave the roof a bit too much which hid all the detail. So I got a cotton with some thinners on and removed the paint from around the heads of the Scale Hardware bolts in the roof of the cab. It has lost a little of the black, but this engine is going to be filthy dirty so the weathering will hide where the primer is coming through.
In terms of how filthy, something like this http://www.phantasrail.co.uk/Sid/Gold0280t.JPG would be nice to achieve, maybe even a little heavier. I love all the big white streaks and patches on the smokebox that come from too much priming of the cylinders, and big white patches on the lead driving wheels from where the steam from the cylinders emulsifies the oil on the wheels !!
I need to do have a bit of practice on some ropey old models before i take to any of the 3 engines..
JB.