Decanting Small Amounts from Rattlecans

[bobthehobbyguy]

Some good info. Learned a couple of things from the videos.

The length of videos was reasonable as they are created to address those that haven't done the process before. Also all the required caveats so people won't injure themselves or damage their property and then complain they weren't warned.

[Swinger 340]

I have found if I put a toothpick in the jar of paint I have just decanted it seems to help the gassing out go a little quicker. You can see the paint start to bubble around the toothpick.

[Michael jones]

From my experience no need to do any of the things listed above, just spray from the can straight into the side of the airbrush cup and straight onto your model. Done it hundreds of times! Especially good with tamiya spray cans as makes no mess at all(of course I have not tried every brand of spray can!). No need for extra bottles or straws. Just do it carefully and all will be grand. No need to wait for off gassing either, as that is how it always comes out of the can anyway if sprayed directly onto your model, so no different through an airbrush. The best place to store paint is in the original spray can. 

[Pete J.]

Hey Richard, I've been doing this a very long time and use a totally different method than most.  I will describe it after I answer your question.

It is always best to let decanted paints sit for a time.  The propellent that most manufactures use is propane for various reasons.  While is it under pressure in the can, it dissolves into the paint and takes time to "de-gas" when pressure is released even in small amounts.  The most common problem with painting decanted paints with an airbrush, Tamiya paint in particular, is that the paint flashes(or the top sets first) and the gas trapped below that skin creates bubbles.  I find that is happens most often in areas that the paint accumulates, like panel lines or where two parts create a vertical and horizontal surface, like wings of aircraft meeting the fuselage.  In that case the paint takes a lot longer to degas and the bubbles show up long after you can do anything about it. 

So  yes, let is sit.  Frankly, I am a super cautious person and let is sit overnight.  I also tend to decant an entire can at one time as Tamiya's rattle cans will just fit in one of their 46ml mixing jars perfectly.  So far I have found this is cheaper than buying their new LP paints. (Same paint without the can)

Now as I mentioned, I decant very differently than others. I started by poking holes in the side of cans with an ice pick.  That could get really exciting very fast, but I found I could control the release of the propellent by slowly withdrawing the tapered ice pick to act like a valve. The real problem with that was that you had to stand there with a cloud of propane around you for a long time until the majority of the propellent was released.  I tried to come up with some sort of saddle valve that would penetrate the can and control the flow.  After a lot of trial and stupidity, not to mention paint all over, I came up with my own tool.

  Then I happened to be at an automotive A/C repair shop and saw them using a "side can penetrating" tap.  It is a tool that looks like a hand held clamp with a gas valve that they use to put liquid refrigerant into an ac system from a can.  Bingo! Just what I wanted.  A tool designed to punch a hole in a rattle can and create a controlled release of the gas inside.  

  So to finish this method,  I use the refrigerant tool to punch a hole near the top of the can and set the valve to slowly release the propellent.  I lay the can and the tool on it's side on the bench and leave it overnight.  The next day I come back and shut the valve and shake the heck out of the can to mix the paint.  I release the tool and get out my trusty ice pick and with the can on it's side and the first hole straight up, I punch another hole as close to the bottom as I can.  I then put my fingers over both holes and stand the can up.  I hold the bottom hole over the jar and release my finger from the bottom hole.  I then slowly release the top hole to control the flow. 

 Once I have all the paint out, I use a pipet to squirt some Tamiya lacquer thinner into the can through one of the holes, cover the holes with my fingers and and shake it up.  This gets the last little bit of paint out of the can.  I told you I am cheap!

Oh and one last tip. When the can is empty, tear open the side with a can opener.  You will find two small glass marbles inside.  Take them and drop them in the jar to help mix up the paint when you want to use it again.  

[Bills72sj]

Richard, My procedure is almost identical to Pete's above. I made my own piercing tool from a stainless steel turbo intake clamp and an old clamp on automotive refrigerant can piercer. Once pierced, I can throttle and direct the propellent flow with the valve and the hose. I let the can sit for half a day to outgas. I then use a strong pocket knife to cut he can open and pour out the paint into a jar. I too save the marbles. I have learned that the shelf life of decanted paint is limited to less than a week unless you want to keep adding paint solvents to it. Just have your parts ready first and then decant the paint a day or so before you want to paint them. Below is a picture of the tool I made. The tool greatly reduces the risk of making a mess.

Edited December 7, 2021 by Bills72sj

[Snake45]

9 hours ago, Pete J. said:

Hey Richard, I've been doing this a very long time and use a totally different method than most.  I will describe it after I answer your question.

It is always best to let decanted paints sit for a time.  The propellent that most manufactures use is propane for various reasons.  While is it under pressure in the can, it dissolves into the paint and takes time to "de-gas" when pressure is released even in small amounts.  The most common problem with painting decanted paints with an airbrush, Tamiya paint in particular, is that the paint flashes(or the top sets first) and the gas trapped below that skin creates bubbles.  I find that is happens most often in areas that the paint accumulates, like panel lines or where two parts create a vertical and horizontal surface, like wings of aircraft meeting the fuselage.  In that case the paint takes a lot longer to degas and the bubbles show up long after you can do anything about it. 

So  yes, let is sit.  Frankly, I am a super cautious person and let is sit overnight.  I also tend to decant an entire can at one time as Tamiya's rattle cans will just fit in one of their 46ml mixing jars perfectly.  So far I have found this is cheaper than buying their new LP paints. (Same paint without the can)

Now as I mentioned, I decant very differently than others. I started by poking holes in the side of cans with an ice pick.  That could get really exciting very fast, but I found I could control the release of the propellent by slowly withdrawing the tapered ice pick to act like a valve. The real problem with that was that you had to stand there with a cloud of propane around you for a long time until the majority of the propellent was released.  I tried to come up with some sort of saddle valve that would penetrate the can and control the flow.  After a lot of trial and stupidity, not to mention paint all over, I came up with my own tool.

  Then I happened to be at an automotive A/C repair shop and saw them using a "side can penetrating" tap.  It is a tool that looks like a hand held clamp with a gas valve that they use to put liquid refrigerant into an ac system from a can.  Bingo! Just what I wanted.  A tool designed to punch a hole in a rattle can and create a controlled release of the gas inside.  

  So to finish this method,  I use the refrigerant tool to punch a hole near the top of the can and set the valve to slowly release the propellent.  I lay the can and the tool on it's side on the bench and leave it overnight.  The next day I come back and shut the valve and shake the heck out of the can to mix the paint.  I release the tool and get out my trusty ice pick and with the can on it's side and the first hole straight up, I punch another hole as close to the bottom as I can.  I then put my fingers over both holes and stand the can up.  I hold the bottom hole over the jar and release my finger from the bottom hole.  I then slowly release the top hole to control the flow. 

 Once I have all the paint out, I use a pipet to squirt some Tamiya lacquer thinner into the can through one of the holes, cover the holes with my fingers and and shake it up.  This gets the last little bit of paint out of the can.  I told you I am cheap!

Oh and one last tip. When the can is empty, tear open the side with a can opener.  You will find two small glass marbles inside.  Take them and drop them in the jar to help mix up the paint when you want to use it again.  

Very interesting, thanks Pete! 

[NOBLNG]

9 hours ago, Pete J. said:

It is always best to let decanted paints sit for a time.  The propellent that most manufactures use is propane for various reasons.  While is it under pressure in the can, it dissolves into the paint and takes time to "de-gas" when pressure is released even in small amounts.  The most common problem with painting decanted paints with an airbrush, Tamiya paint in particular, is that the paint flashes(or the top sets first) and the gas trapped below that skin creates bubbles.  I find that is happens most often in areas that the paint accumulates, like panel lines or where two parts create a vertical and horizontal surface, like wings of aircraft meeting the fuselage.  In that case the paint takes a lot longer to degas and the bubbles show up long after you can do anything about it. 

So why doesn’t this same scenario occur when painting a model directly from the can? Just curious.🤔

[Pete J.]

1 hour ago, NOBLNG said:

So why doesn’t this same scenario occur when painting a model directly from the can? Just curious.🤔

I am having some trouble understanding your question.  If you mean why isn't there an issue in the can, it is because it is all pressurized in the can.  When you decant it to brush or airbrush it, without letting it "rest" the paint acts like it is boiling and makes a mess.  There is enough propellent left in solution right after your decant it that if you put in a closed container it will pressurize the container.  When you open the container, it suddenly releases the paint or 'blows up".  The same thing that would happen if you opened a one inch hole in the side of the can.  

  If you are asking about bubbling in the finish, it does happen.  That is the primary reason that most people recommend a series of light coats.  I don't know how many times I have had bubbles show up in crevasse in the model with rattle cans.  

[Bainford]

5 hours ago, NOBLNG said:

So why doesn’t this same scenario occur when painting a model directly from the can? Just curious.🤔

I think it has to do with the dynamic of the paint delivery. Inside the can there is a high pressure atmosphere which pushes the paint out of the can and through the nozzle. The paint remains under pressure and has no chance for gas release until it leaves the nozzle. With an airbrush the paint begins to flow when a low pressure is induced in the mixing/venturi chamber, putting the paint in a condition of lower pressure right away when the trigger is pressed, and considerably more so when it incurs the low pressure of the chamber. This lower pressure tries to 'pull' the gas out of the paint, or perhaps more accurately, gives it a stronger incentive to leave the paint.

In both cases, paint flow is induced by a pressure differential. I think the key element is that in the can, the paint flows due to a pressure 'up stream' of the paint greater than ambient pressure. In the airbrush, the pressure differential is due to a pressure lower than ambient pressure 'down stream' of the paint.

This reduced pressure in the airbrush chamber causes the gas to escape the paint in volume, screwing up the flow dynamics with the airbrush and generally making a bubbly mess. This will be much more of a problem with a siphon feed airbrush than a gravity feed, and may pose even less of a problem with an external mix airbrush. It's worth noting that even with a spray can, the problem can still exist. Sometimes, especially in grooves and crevices where paint build-up is significant, tiny pin holes can be spotted when the paint is dry. This is due to de-gassing.

Edited December 7, 2021 by Bainford
bats in the belfry

[Michael jones]

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Edited December 7, 2021 by Michael jones

[Bainford]

2 hours ago, Michael jones said:

Have you ever actually tried spraying from the can directly into your airbrush and straight onto the model? Absolutely no problems at all. I do this all the time(done hundreds of times!). It works perfect. Whatever you are talking about must be a theory, as from my experience this doesn't happen. I use a gravity feed airbrush and mostly Tamiya spray cans (but not always) btw.

Hi Michael. See my Nov 17 post in this thread, about half way down the first page. I incurred a de-gassing induced failure every time when the paint was not given time to de-gas. So have others over the years. Like many aspects of painting, there are many variables that can effect the degree to which problems will or will not be experienced by an individual. I think your suggestion that there will be 'absolutely no problems at all' is a slightly short sighted because some experienced painters have incurred problems of this nature. Indeed, it is why the OP, a highly experienced builder himself, started this post. So the fact is, in some circumstances, it can happen.

Edited December 7, 2021 by Bainford

[NOBLNG]

1 hour ago, Bainford said:

I think it has to do with the dynamic of the paint delivery. Inside the can there is a high pressure atmosphere which pushes the paint out of the can and through the nozzle. The paint remains under pressure and has no chance for gas release until it leaves the nozzle. With an airbrush the paint begins to flow when a low pressure is induced in the mixing/venturi chamber, putting the paint in a condition of lower pressure right away when the trigger is pressed, and considerably more so when it incurs the low pressure of the chamber. This lower pressure tries to 'pull' the gas out of the paint, or perhaps more accurately, gives it a stronger incentive to leave the paint.

In both cases, paint flow is induced by a pressure differential. I think the key element is that in the can, the paint flows due to a pressure 'down stream' of the paint greater than ambient pressure. In the airbrush, the pressure differential is due to a pressure lower than ambient pressure 'up stream' of the paint.

This reduced pressure in the airbrush chamber causes the gas to escape the paint in volume, screwing up the flow dynamics with the airbrush and generally making a bubbly mess. This will be much more of a problem with a siphon feed airbrush than a gravity feed, and may pose even less of a problem with an external mix airbrush. It's worth noting that even with a spray can, the problem can still exist. Sometimes, especially in grooves and crevices where paint build-up is significant, tiny pin holes can be spotted when the paint is dry. This is due to de-gassing.

So, in a nutshell, the can pushes the paint out, and the airbrush pulls the paint out. I can see the method of puncturing the can and slowly releasing the pressure allowing more propellant to remain in the paint. I think spraying the paint through a straw in order to decant it allows a lot more of the propellant to escape initially. A secondary spraying through the air brush has always relieved the rest of it in my experience. I spray it into a siphon bottle and use an external mix airbrush, which may or may not factor in? This could be like the red plastic bleed problem….some folks experience it and some don’t. I’m not denying that it can happen, just that some condition or procedure is different.🤷‍♂️

 

Edited December 7, 2021 by NOBLNG

[Bainford]

41 minutes ago, NOBLNG said:

So, in a nutshell, the can pushes the paint out, and the airbrush pulls the paint out.

 

That's the gist of it, though the physics minded among us will quickly point out that in both cases the paint is being pushed out. The mechanism is different though, where the airbrush operates at a much lower internal pressure, and I think that is the key. The lower pressure inside the airbrush allows the gas to readily escape, and it happens at the point where the paint and air combine, destabilizing this delicate balance. A siphon feed airbrush requires a stronger vacuum signal (lower pressure) in the chamber than a gravity feed, as it has to not only move the paint, but has to provide the motive force to first lift it up from the bottle, so the problem is worse with a siphon feed. I believe this is also why external airbrushes are less susceptible to this phenomenon. There is no mixing inside of a low pressure chamber, the mixing all happens outside of the airbrush, though the venturi effect is used to do this in all airbrushes. With the external airbrush I suspect that there is probably still rapid de-gassing at the point of mixing as the lower pressure of the venturi is encountered, but the dynamics of the external mix does not significantly destabilize the mix.

That's my take on it anyway.

[Michael jones]

4 hours ago, Bainford said:

Hi Michael. See my Nov 17 post in this thread, about half way down the first page. I incurred a de-gassing induced failure every time when the paint was not given time to de-gas. So have others over the years. Like many aspects of painting, there are many variables that can effect the degree to which problems will or will not be experienced by an individual. I think your suggestion that there will be 'absolutely no problems at all' is a slightly short sighted because some experienced painters have incurred problems of this nature. Indeed, it is why the OP, a highly experienced builder himself, started this post. So the fact is, in some circumstances, it can happen.

The OP never actually stated about having problems. He was asking about decanting and leaving it to sit. Anyway you keep doing what you do, and I will keep having great success with my method.

 

Regards

[Pete J.]

To many paint is a dark art, inhabited by demons and other evil creatures. If you are having success with your methods, keep on doing it.  It works for you and no one is trying to convert anyone. This post suggests a lot of different opinions and methods.  The best one is the one that works for you.  If yours isn't working, try someone elses approach.  Your choice.