The mystery of Humbrol enamels drying in tin

[Beardie]

I always use Humbrol Enamels and have found they suit me well. OK occasionally I will have a tin that refuses to dry properly (I have had this i the past worse when I tried Revell enamels) but apart from this I find them very good but what I have always noticed is that, once the tin reaches a level below about half full they start to form a skin. At first I theorised that this was due to the seal between lid and tin no longer being any good but now I am not convinced this is what is actually happening.

What I now suspect is that there is a point where the amount of oxygen in the tin when the lid is closed is sufficient to oxidise the surface of the paint. Question is...... If this is the case (I am only guessing at this after taking care to try and ensure the lids are well fitted to keep out the air whenever I finish using a tin) then what can be done about it short of keeping the tins in a vacuum when not in use.

[Rob G]

Hmm. I haven't found that at all - since my recent reintroduction to the Fine and Noble Arte of fettling ye Olde Plastic bits, I've been digging into my paint stash a bit, and so far, all seems well. A number of years ago, when I was going to start modelling again (didn't happen, but never mind) I went through all my paints - many Humbrol tins and Tamiya and Gunze Sangyo glass bottles, and a few Xtracylix plastic bottles bought from Hannants Colindale in 2007, and had a pogrom. Anything that had been opened previously was reopened, and either thrown straight out if gummy, or stirred up to check to see if it was still usable - if usable, I cleaned up all the sealing surfaces and resealed the tin or bottle, then back into the drawer it went. So far, everything I've reopened has been usable. The stored away Humbrol Metalcote tinlets however, have leaked a bit, despite being unopened and in their original box (when the LHS closed, they gave me a pile of stuff to pass on to the local club guys, as wanted).

Paint skins when there's sufficient free space above the top surface for the solvent to come out of solution and hang in the air as it were, and I wouldn't think that a Humbrol tinlet would have a big enough free volume to allow enough solvent to do that. It may be that there's a tiny air leak in the lid, that is allowing the solvent to continue its journey out into the atmoshpere, thus causing the paint to skin. I'm probably preaching to the choir, but if you're not already, give the tin edge and the lid a good clean off before you reseal them - that may help. The other thing is to make sure you're not deforming the lid when you remove it - little lifts from a few points around the edge are much better than one big 'pop' from a single point.

Apart from that, I'm out of ideas.

[Andrew Jones]

As said above , probably a tiny air leak in the lid seal , try shaking the tinlets after reesealing and then store upside down.

Andrew

[D1fuN0]

Hiya Beardie

Funny you should mention this...

I have some old Humbrol Authentics, and even some Airfix Paint, and they are still going strong, and they must be, hell, what 30 years old...

They dont get used often, but they are used.

Then, on the other hand, I have some Humbrols that I have bought in the last 3 months that are already starting to harden

Always have the same routine, lids and rims always cleaned, always ensure that the lid is back on tightly and all paint tins have a leeeeetle tiny ball bearing in them.

On the same note, I also have a couple of bottles of Tamiya paint that I got way back in the late nineties that are still going strong.

Steve

[johnd]

Beardie, same problem here. Older paint tins are ok, newer ones become unusable quite quickly, even when they're nowhere near empty. It's not the seal of the lid either. Incidentally, this has also happened to tins of WEM and Xtracolour. It's why there are now more and more acrylics appearing on my shelves.

John.

[sinnerboy]

get yourself a 2 inch G clamp, glue a 1.5 inch washer to the thread end ( I used Gripfill ) then glue a smaller .75 washer to that so that it fits in the Humrol lid recess, and finally glue another 1.5 washer to the fixed end of the clamp.

Put the lid on the tin, place in clamp & tighten...never has a prob with Humbrol drying out since I've made this. will try & post some pictures later when I get a mo

[andym]

get yourself a 2 inch G clamp, glue a 1.5 inch washer to the thread end ( I used Gripfill ) then glue a smaller .75 washer to that so that it fits in the Humrol lid recess, and finally glue another 1.5 washer to the fixed end of the clamp.

Put the lid on the tin, place in clamp & tighten...never has a prob with Humbrol drying out since I've made this. will try & post some pictures later when I get a mo

A toolmakers vice works well too, that's what I use.

HTH

Andy

[Dave Fleming]

Older Humbrol had different solvents to those used these days.

[Pin]

I keep the tins upside down

[Beardie]

I have some humbrol tins that are lord knows how old and they seem to remain useable right to the bottom (The solvent smells suspiciously like genuine turpentine which I have recently been using small amounts of as I have found it actually seems to delay the drying time of the paint and makes it flow better) but the newer ones I have found tend to skin despite my best efforts once the tin starts to empty. Not all colours behave like this but I have noticed it particularly with Matt and Satin Black (One tin skinned the day after opening and it was brand new (I believe it came direct from Airfix) and the pale colours. Normally I clean the rim and lid and once firmly closed I turn the tin upside down to allow paint to fill any airgaps in the lid/rim seal but have still found skinning.

[Head in the clouds.]

Funny that, I was thinking of posting this same subject as I have the same problem, annoying to say the least, I even had a Humbrol Black Wash which after six months and very little use it went much thicker to the point it was dry on the end of the brush within seconds, the Hubrol paints are no better.

[Rob G]

I have some humbrol tins that are lord knows how old and they seem to remain useable right to the bottom (The solvent smells suspiciously like genuine turpentine which I have recently been using small amounts of as I have found it actually seems to delay the drying time of the paint and makes it flow better) but the newer ones I have found tend to skin despite my best efforts once the tin starts to empty. Not all colours behave like this but I have noticed it particularly with Matt and Satin Black (One tin skinned the day after opening and it was brand new (I believe it came direct from Airfix) and the pale colours. Normally I clean the rim and lid and once firmly closed I turn the tin upside down to allow paint to fill any airgaps in the lid/rim seal but have still found skinning.

Hmm. Mine are all older (none younger than 5 years or so, plus whatever time the retailer had it sitting on his shelf), so this is possibly in my future. Is it possibly a result of 'safer' solvents being used in the formulation?

[Beardie]

I think it may be due to the desire to get faster drying, as this is the advantage that Acrylics have. The older natural solvents like turpentine are slower drying and more oily, the upside of this is that the paint has more time to level itself but the downside is that it means a paintjob can't progress as fast and everyone is after speed these days.

I would be interested to talk to an expert in Alkyd "enamel" formulation about all the aspects of these paints. It is a funny thing that, if you look at Alkyd's in the art world - Griffin alkyd by Winsor and Newton for example they say that depending on thickness of paint it should be "x" number of weeks or even months before it is varnished. I am not sure if Alkyd resins "dry" in quite the same way as traditional linseed oil based paints, that is, do they absorb oxygen from the atmosphere in the same way to form a stable skin? Obviously if this is the case sealing them in too early with a varnish could result in an unstable finish.

When you think about how much care we take over building a model you would assume that it would follow that we would be just as careful and knowledgeable about the all important operation of applying it's colourful skin but even from the manufacturers the information about handling their paints is very limited and patchy at best.

[Troy Smith]

I think it may be due to the desire to get faster drying, as this is the advantage that Acrylics have. The older natural solvents like turpentine are slower drying and more oily, the upside of this is that the paint has more time to level itself but the downside is that it means a paintjob can't progress as fast and everyone is after speed these days.

I would be interested to talk to an expert in Alkyd "enamel" formulation about all the aspects of these paints. It is a funny thing that, if you look at Alkyd's in the art world - Griffin alkyd by Winsor and Newton for example they say that depending on thickness of paint it should be "x" number of weeks or even months before it is varnished. I am not sure if Alkyd resins "dry" in quite the same way as traditional linseed oil based paints, that is, do they absorb oxygen from the atmosphere in the same way to form a stable skin? Obviously if this is the case sealing them in too early with a varnish could result in an unstable finish.

When you think about how much care we take over building a model you would assume that it would follow that we would be just as careful and knowledgeable about the all important operation of applying it's colourful skin but even from the manufacturers the information about handling their paints is very limited and patchy at best.

If Alkyd paint uses 'drying oils'

http://en.wikipedia.org/wiki/Drying_oil

A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen

It could be modern paint starts to cross link fast, meaning it will begin to 'gel' with not much solvent evaporation.

A possible way to stop the drying out is to add a few drops of some solvent on top before resealing the can, creating an atmosphere above the paint that is 'saturated' with solvent, stopping solvent evaporation from the paint?

Perhaps the 'zippo' type lighter fuel would be good for this, as it is very volatile.

The chap who would most likely know the details is Nick Millman though.

[Beardie]

The addition of a few drop of solvent to the top of the paint before storage may well be a good idea. I think I will give it a try.

Hmmm just been reading the wikipedia entry on Alkyds and, although I can't really make head nor tail of it properly as I don't have a chemistry background it does seem to suggest there has been a shift in the alkyd resin used to "short-oil A/D resin" which apparently gives better durability, it does also say that acrylic resin is also sometimes used in the mix these days. I wonder if this is what makes the difference between the older and newer paint characteristics. I guess paint drying can be slowed down again by addition of a tiny quantity of refined Linseed or Poppy drying oil which are used with Alkyds in the art world but that may slow down drying of the paint quite considerably.

[viscount806x]

I'm wondering if simply adding some old style 'proper' turpentine might be the answer. I'm still using this for thinning enamels for airbrushing and I usually decant any excess back into the tinlet if there is space. I've not had any reason to use any recent enamels (but have them standing by) and it will be interesting to experiment with them when the time comes. Drying up of paint in storage is something which we shouldn't have to put up with though is it? How can any serious modeller not have spare paint put by for a rainy day?

What is/was wrong with the original formulae? Is it the case of the dreaded H&S again running the show and insisting on the non use of certain substances?

As an aside, I've just this week sprayed a vintage Frog Beaver with a 30+ year old Gloy tinlet, sealed since new and thinned with turpentine. Good as gold but needs at least a week to 'gas off' before the next step.

[Beardie]

I have noticed myself, quite by accident, that Humbrol enamel seems to behave itself much better with real turpentine than it does with either Humbrol thinners or white spirit although it does definitely take longer to dry.

[viscount806x]

I have noticed myself, quite by accident, that Humbrol enamel seems to behave itself much better with real turpentine than it does with either Humbrol thinners or white spirit although it does definitely take longer to dry.

As I said above, that is what I use for thinning but white spirit for any cleaning up. I read many moons ago (at least 35-40 years) that proper turpentine should always be used for thinning enamels, the reason is lost to me now but it was quite specific advice at the time. Less aggressive perhaps? Certainly though it does smell a bit and needs adequate drying time, I leave at least untill I can no longer smell it when held close to my hooter. Often up to a week.

[Troy Smith]

As I said above, that is what I use for thinning but white spirit for any cleaning up. I read many moons ago (at least 35-40 years) that proper turpentine should always be used for thinning enamels, the reason is lost to me now but it was quite specific advice at the time. Less aggressive perhaps? Certainly though it does smell a bit and needs adequate drying time, I leave at least untill I can no longer smell it when held close to my hooter. Often up to a week.

White Spirit is cheaper, hence it's wider use.

http://en.wikipedia.org/wiki/White_spirit

note

Mineral turpentine is chemically very different from turpentine, which mainly consists of pinene, and it has inferior solvent properties.[8][not in citation given] Artists use mineral spirits as an alternative to turpentine since it is less flammable and less toxic. Because of interactions with pigments, artists require a higher grade of mineral spirits than many industrial users, including the complete absence of residual sulfur.

Mineral spirits have a characteristic unpleasant kerosene-like odor. Chemical manufacturers have developed a low odor version of mineral turpentine which contains less of the highly volatile shorter hydrocarbons.[9] Odorless mineral spirits are mineral spirits that have been further refined to remove the more toxic aromatic compounds, and are recommended for applications such as oil painting, where humans have close contact with the solvent.

So higher grades of white spirit may work better.

I have used Turpentine for thinning house paint as it works better, paint flows better, less greasy and faster evaporation than white spirit.

http://en.wikipedia.org/wiki/Turpentine

The two primary uses of turpentine in industry are as a solvent and as a source of materials for organic synthesis. As a solvent, turpentine is used for thinning oil-based paints, for producing varnishes, and as a raw material for the chemical industry. Its industrial use as a solvent in industrialized nations has largely been replaced by the much cheaper turpentine substitutes distilled from crude oil.

The other solvent worth trying is lighter fuel, it's 'light petrol' and very volatile, so you can thin paint right down, but the solvent evaporates quickly, why it's used for oil washes.

So if you enamels are you thing, I'd say Turpentine is the way to go, maybe with a bit of lighter fluid.

Marty, remember you can use your oil paints as well, great for washes and many figure painters use them, also the 'dot wash' technique used more for armour but also on aircraft.

http://www.swannysmodels.com/yabb2/YaBB.pl?num=1247064115

http://www.militarymodelling.com/forums/postings.asp?th=40872

http://www.ipmshawaii.0catch.com/techniques_dot_filtering.html

These are some of the first hits from google, but there are demonstrations on youtube I'm sure.

Usual caveats, try it on a scrap kit first.

cheers

T

[Bonehammer]

I have started giving Humbrol tins a couple light bumps with a flat-face hammer once I close them. They remain open-able and no lid has been popping open after a few hours of sitting as it used to occur. Will tell you how it works.