Substitute for Chipping Medium?

[Inquisitor Eisenhorn]

I am trying to do the thing where I do a rusted metal layer, then put some sort of chipping resistant medium over it, and then put a second layer of different paint over it and scratch it up to reveal the rusted undercoat. 

 

I don't have properly labeled chipping medium, but would some sort of spray varnish do at least a semi-decent job sealing the undercoat to make it resistant to scratches to the overcoat?

[Arkhanist]

You need both varnish and a chipping medium.

 

The varnish coat goes over the rusty underlayer to protect it; let it properly dry (usually several hours, minimum). Then the chipping fluid, let dry for say 10-20 minutes, then the top colour coat and let dry for another 10 to 20 minutes. The idea is the chipping medium layer is quite weak when freshly dried, and thus can be removed by scratching/rubbing with e.g. a damp toothbrush or stiff brush, taking the top coat with it and revealing the rusty underlayer in those scratches.

 

Without the varnish layer, the physical scratching can also accidentally remove the rusty underlayer too, and go through to primer or even bare plastic. Once you're happy with the final effect, give it another thin varnish coat to help protect it from further weathering by accident, and give it a while to fully dry - this will also allow the chipping fluid to dry stronger.

 

The old method before chipping medium existed was to use hairspray, i.e. spray that on the dry varnish before the top coat colour. The performance of hairspray is less predictable - it can be easier or harder to remove than chipping fluid depending upon the hairspray strength, and how long you leave it before scratching, so some experimentation first is a good idea. Stronger hairspray tends to lead to easier/heavier chipping, so you need to be careful not to overdo it.

 

Be advised that it's best to airbrush or spraycan the top coat, as brush painting it on will tend to activate the chipping fluid/hairspray early and mess up getting a good top coat. Spraying the rust layer, varnish and chipping fluid are optional, but easiest to airbrush if you have one.

 

Here's a video comparing AK heavy chipping fluid vs good old hairspray.

 

Edited August 20, 2020 by Arkhanist

[Inquisitor Eisenhorn]

Wow thanks for the detailed response! Now I know how I'll proceed.

[Lovecraft0110]

I am trying to do the thing where I do a rusted metal layer, then put some sort of chipping resistant medium over it, and then put a second layer of different paint over it and scratch it up to reveal the rusted undercoat. 

 

I don't have properly labeled chipping medium, but would some sort of spray varnish do at least a semi-decent job sealing the undercoat to make it resistant to scratches to the overcoat?

You could try liquid mask chipping, which I demonstrate in this video:

 

[Bung]

Or you can do Salt weathering.

Wer tge varnished surface with water and sprinkle Salt on the surface. Let it dry and Spray your next color like with the chipping medium.

You can removed the Salt with a stiff brush when tge color is dry.