Airbrushing exhaust stains

[Spitfire 123]

Hi all,

Does anyone here know a good video on how to airbrush exhaust stains on aircraft? Any good tips anyone has for doing this would also be very much appreciated. 

Thanks in advance,

Riley

[Mark Harmsworth]

This doesn't answer your question directly but a while ago I decided that using an airbrush for exhaust (and gun) stains was too tricky for me and required more cleaning of the airbrush (not my favourite job). So I started using pastel chalks and haven't regretted that at all - in fact it's one of the little tasks that I enjoy.

 

Are you definitely going the airbrush route?

Mark

[Ray_W]

Hi Riley, 

 

I recently described my method as follows for this build:

 

The smoke stain is simply a Tamiya Flat Black and Nato Brown mix, thinned with Gunze's Aqueous Color Thinner (I suppose similar to Tamiya X-20A). Ratio was a bit of this and that until I achieved something not black but a touch reddish brown. I sprayed it through my Iwata HP-B Plus 0.2 needle. Pressure, if you can believe my gauge, 12 psi. Built up with narrow streaks close to the surface. Airbrush always moving. Often start the paint flow on my gloved hand to ensure I have the quantity I want and my trigger control is in order.  If unsure, attach a piece of paper or tape close to your spraying location and go to that to check spray. I find this handy also with mottling.  Darn hard to see on the aircraft until it's too late. Key thing, again, airbrush never idle to avoid pooling in a location.

 

 

 

A couple of other pointers.

 

I always study the prototype's photos to try and replicate what I see so. It might not to be as heavy as the Bf-110 above (these 110's did get heavy exhaust staining and also seem to pick up the exhaust stain on the fin). I might also use a dirty light grey if appropriate or light grey with dark highlights. I may even put down grey and then a dark mix or vice versa. I like the Tamiya acrylics for the job as they dry ultra flat. This job is one of the last for me, that is after your finish coat. It is what makes scale modelling an adrenalin sport. Grab some colours and experiment with a mix.

 

How thin? Answer is thin. I just poured some out into a tray to give an idea. This is the mix described previously. I will thin this just a fraction more when ready to use as some of the solvent has evaporated from my pre-mix. Not much it is just about there. Always better thin and build colour slowly.  Keep your airbrush moving to prevent pooling.

 

 

Gradually build up the colour moving the airbrush close to the surface along the line you want. I am about 5 to 15 mm off the surface with the airbrush always moving and at some speed. Slowly build the effect.  If you can't see colour on the model do not stop the airbrush movement. Do some practice on a white card to get the feel for the required distance and speed and colour build-up. Very difficult to see on the model until it is too late. 

 

I start at the exhaust (usually) and drag back along the required flow line. I will then often jump in at other areas of the smoke trail if need be. The process takes multiple passes, minimum 3 though typically more than 5, yet it is quick.

 

The back of my gloved hand, that is the one holding the model, is covered with practice exhaust squiggles. I am continually practicing as I go. Need that eye-hand co-ordination. The colour build slowly and hence is controllable.

 

I find with my mix, that it will often dry darker. My usual practice is to hit it with a hair dryer after a few passes to accelerate the drying so I can check if it is to my satisfaction.

 

Note that I now use a 0.2 mm needle, but was able to get good exhaust staining with a 0.35 mm. It is just a matter of practice and frankly not a lot is required. My pressure is a little higher than some quote. Trigger control with the Iwata's is excellent, with some practice, so I find this compensates. Do not be afraid to run at a lower pressure if you're more comfortable. Soon you will be playing around with different effect moving airbrush in leaving the surface. Going in closer as need be.

 

IMPORTANT POINTER with ultra thin mixes with dual-action airbrushes. Always ensure paint is closed before air otherwise you may get a splatter when you start the next line. That is - air on, paint on, paint off, air off. if you need to drop the trigger and can't get the "paint off air off" process working, then start some "air only" off the kit before your next line. 

 

Last point, expect disasters. You learn the best airbrush skills with the repair jobs.

 

Ray

 

  

[dogsbody]

Just remember that the Allies used 100+ octane petroleum-based fuels that had a fairly high TET content that left the exhaust stains quite grey.

The Germans, on the other hand, didn't have access to as much petroleum and made a lot of their fuels from coal-tar distillate. This left a very dark, almost black exhaust stain.

I'm not sure about what the Japanese and Russians had.

 

 

 

Chris

[Spitfire 123]

On 20/03/2021 at 21:37, Mark Harmsworth said:

This doesn't answer your question directly but a while ago I decided that using an airbrush for exhaust (and gun) stains was too tricky for me and required more cleaning of the airbrush (not my favourite job). So I started using pastel chalks and haven't regretted that at all - in fact it's one of the little tasks that I enjoy.

 

Are you definitely going the airbrush route?

Mark

Hi Mark, thanks for the reply. That sounds like a good method, and I will be sure to try it. Do you just scrape some of the pastel off and then brush it on?

Thanks again, 

Riley

[Spitfire 123]

On 21/03/2021 at 19:13, Ray_W said:

Hi Riley, 

 

I recently described my method as follows for this build:

 

The smoke stain is simply a Tamiya Flat Black and Nato Brown mix, thinned with Gunze's Aqueous Color Thinner (I suppose similar to Tamiya X-20A). Ratio was a bit of this and that until I achieved something not black but a touch reddish brown. I sprayed it through my Iwata HP-B Plus 0.2 needle. Pressure, if you can believe my gauge, 12 psi. Built up with narrow streaks close to the surface. Airbrush always moving. Often start the paint flow on my gloved hand to ensure I have the quantity I want and my trigger control is in order.  If unsure, attach a piece of paper or tape close to your spraying location and go to that to check spray. I find this handy also with mottling.  Darn hard to see on the aircraft until it's too late. Key thing, again, airbrush never idle to avoid pooling in a location.

 

 

 

A couple of other pointers.

 

I always study the prototype's photos to try and replicate what I see so. It might not to be as heavy as the Bf-110 above (these 110's did get heavy exhaust staining and also seem to pick up the exhaust stain on the fin). I might also use a dirty light grey if appropriate or light grey with dark highlights. I may even put down grey and then a dark mix or vice versa. I like the Tamiya acrylics for the job as they dry ultra flat. This job is one of the last for me, that is after your finish coat. It is what makes scale modelling an adrenalin sport. Grab some colours and experiment with a mix.

 

How thin? Answer is thin. I just poured some out into a tray to give an idea. This is the mix described previously. I will thin this just a fraction more when ready to use as some of the solvent has evaporated from my pre-mix. Not much it is just about there. Always better thin and build colour slowly.  Keep your airbrush moving to prevent pooling.

 

 

Gradually build up the colour moving the airbrush close to the surface along the line you want. I am about 5 to 15 mm off the surface with the airbrush always moving and at some speed. Slowly build the effect.  If you can't see colour on the model do not stop the airbrush movement. Do some practice on a white card to get the feel for the required distance and speed and colour build-up. Very difficult to see on the model until it is too late. 

 

I start at the exhaust (usually) and drag back along the required flow line. I will then often jump in at other areas of the smoke trail if need be. The process takes multiple passes, minimum 3 though typically more than 5, yet it is quick.

 

The back of my gloved hand, that is the one holding the model, is covered with practice exhaust squiggles. I am continually practicing as I go. Need that eye-hand co-ordination. The colour build slowly and hence is controllable.

 

I find with my mix, that it will often dry darker. My usual practice is to hit it with a hair dryer after a few passes to accelerate the drying so I can check if it is to my satisfaction.

 

Note that I now use a 0.2 mm needle, but was able to get good exhaust staining with a 0.35 mm. It is just a matter of practice and frankly not a lot is required. My pressure is a little higher than some quote. Trigger control with the Iwata's is excellent, with some practice, so I find this compensates. Do not be afraid to run at a lower pressure if you're more comfortable. Soon you will be playing around with different effect moving airbrush in leaving the surface. Going in closer as need be.

 

IMPORTANT POINTER with ultra thin mixes with dual-action airbrushes. Always ensure paint is closed before air otherwise you may get a splatter when you start the next line. That is - air on, paint on, paint off, air off. if you need to drop the trigger and can't get the "paint off air off" process working, then start some "air only" off the kit before your next line. 

 

Last point, expect disasters. You learn the best airbrush skills with the repair jobs.

 

Ray

 

  

Hi Ray, thanks for the reply, much appreciated. I love how it came out on the bf 110. You have definitely answered my question, and thanks for all the tips as well!

Many thanks, 

Riley

[Mark Harmsworth]

14 hours ago, Spitfire 123 said:

Hi Mark, thanks for the reply. That sounds like a good method, and I will be sure to try it. Do you just scrape some of the pastel off and then brush it on?

Thanks again, 

Riley

I use artists pastel chalks and have two sets  - one with a range of grey pastels and one with browns. I use a small piece of sandpaper and rub the chalk onto that. An old brush then applies it to the model - a cotton bud works well too. Having the range of browns and greys allows me to build up a slightly varied stain. You can buy packs of modelling pastel chalks ready for use but my pastel chalks will last me forever.

Mark