Everything you want to know about Paint
The purpose of this write up is to give you a primer (pun intended!) in paint, what paint is, the different types, cross compatibility, etc. Our entire hobby is built around paint and plastic, yet so many of us use paint without entirely knowing what it is and how it works. Once you know what paint is, then you can start using it effectively on your model. This is just meant to be a rough guide, I am well aware you can get away with breaking some of the guidelines in here without screwing up your paint job..
Paint - What is it?
Think about, for a minute, a bottle of Elmer's white glue. Pour out a drop of it onto a piece of paper and let it dry. What will happen? It will dry into a film of something hard and clear. When you put some water on it, you can wash it off. That's exactly what paint is like - except with color!
Paint is made up of three parts, the solvent, carrier, and pigment (these may not be the official terms). First, the most important part. The pigment is, basically, color. Molecules of color. But most of the time, it's not 'sticky'. If you chopped a crayon into little flakes and sprinkled it onto a piece of paper, it wouldn't stick right? But what if you poured glue on the paper first? Then it would stick, right?
That's what the carrier is. The pigment is bonded chemically to the carrier, and the carrier is the 'glue' that attaches to the surface of the plastic, keeping the pigment with it.
The third part, solvent, is what gives us the different 'types' of paint: lacquer paints,
enamel paints, acrylic paints. Going back to the Elmer's glue analogy, it's like 'water'; it keeps the pigment and carrier dissolved.
Lacquer,
enamel,
acrylic; these all mean the type of chemicals used to keep the pigment and carrier liquid. Once this stuff dries off, then your paint is 'dry'. It's also what makes paint smell, and makes you hallucinate and get headaches from if you smell too much of it.
A cool thing about solvents is that the stronger the solvent is, the more types of paint it can help 'thin'. When you thin a paint, you make it 'thinner' so that it can be sprayed easily through an airbrush, or brushed on better, etc. A solvent can only thin a paint if it's able to dissolve the pigment and carrier. You couldn't use water to thin lacquer paint, for example, because the water just can't dissolve the carrier and pigment.
There are other 'ingredients' added to paint as well. These include 'leveling agents' that affect the way the paint dries, making it gloss, semi gloss, or flat. There are also metal flakes or mica particles, which make a color metallic. Pearls fall into this category as well.
Why do I need to wait for it to be cured? Why cant I polish it as soon as it feels dry?
Think about your shoe and the shoelaces on it. If your laces were tangled together, and you tried to pull them apart, you'd find you would be unable to because they're tangled together. This is the same thing with paint, at the molecular level. You have long 'strings' of paint and carrier molecules that are suspended in the solvent. After the solvent dries up, the strings of paint and carrier molecule start tangling up, or as its called, cross-linking. This causes the paint to become tough. The less solvent there is, the tougher the paint becomes. The tougher the paint becomes, the better you can polish and cut it to get that mirror shine. That's why you must wait for it to cure!
How do I know when its done curing?
There is no real way to know if paint is completely done curing, but through extensive testing, there are guidelines that exist for every type of paint. Different brands and types of paint require different times to cure. For example, lacquers can cure in a few days, but
enamels may require weeks to month, and acrylics just as long. It also depends on the temperature you keep it at.
A general test you can try is the smell test. Smell the surface of the paint. If it doesn't smell like 'paint', then you know it's done, or close to done curing. This is because you can't smell the solvent - remember from above? - evaporating, which means there isn't much solvent left on the model. This is the most non invasive procedure. You can, for example, press really hard with your finger and see if it leaves a thumb print - but if you were wrong and it left a thumb print, then you might have to re-spray!
The best way to cure paint is to invest some money in a food dehydrator. A food dehydrator does exactly that - 'dehydrates' the paint of its solvent through heat. A solvent evaporates when you apply heat to it. So the more heat you apply, the faster the solvent evaporates, right? That's why a food dehydrator is useful. Some members of our forum can bang out a completed model from start to finish in a day, thanks to this handy device. You can get one for as little as $40 at amazon.com, or check your local kitchen stores, or, do a search on the forum! There's already been a great topic by freakray.
Misting - What is it?
Misting refers to the practice of spraying on a 'mist' coat, so that you cover the model with fine droplets of paint, but never enough to actually cover the underlying plastic or primer. The purpose of this, is that when you mist, lower amounts of solvents than usual land on the model. The solvent can evaporate before it has a chance to do some damage, leaving the carrier and pigment. Enough mist coats, and you've built a layer of carrier and pigment, with very little damage to the underlying plastic. Such, when you spray your wet coat to get that glossy look, you won't be melting the plastic, only the barrier layer you laid down with the mist coats.
Gloss, semigloss, flat - what does it mean?
Ever hear the term 'smooth as glass'? Touched a piece of glass before? How about this, you're minding your own business when all of a sudden somebody's watch blinds you, because the glass face of the watch reflected sunlight into your eye. Well that's what gloss, semigloss, and flat means. Gloss simply means the paint was designed to dry as smooth as possible. The smoother the paint, the more glossy it is, the more light it reflects, the closer to a 'mirror' it gets. Semigloss is when it reflects some light but scatters the rest. Flat is when it doesn't reflect any light at all. Semigloss and flat paints do this by being designed to dry bumpy and irregular, not smooth.
Polishing paint is just an application of this principle. To get a model to shine, the paint must be smooth. To make the paint smooth, you must sand it and polish it until the surface becomes smooth, if it isn't already smooth.
The importance of primer
Primer serves a multitude of purposes. For one, some paints are translucent - the color they are applied over affects the color of the paint. Try painting red color over black, see how well it goes. A good primer will give a solid base color for the overlying color. In this manner, primers can be almost any color that, when combined with the color coat, would give the desired color. For example, red over white = bright red, red over black = blood red, white over white = white, white over black = grey, etc.
Second, the carrier and pigment of paints usually stick to primer better than plastic. themodelkid says that imagine climbing a wall - you want it to be jutted and cragged so you have something to hold onto, right? Same principle with primer, the paint sticks better to the flat, uneven surface. But don't make it too uneven or it will show through - hence why some people sand their primer with 1500
grit prior to painting.
Third, primers form a protective barrier between the plastic, and some of the harsher paints.
Three diff types of modelling paint
Now for us modelers there are three different types of paint that are used,
lacquer,
enamel,
acrylic. Of course many other types of paint exist, such as polyurethane and whatnot, but they're generally not used much by modelers due to various reasons.
Lacquer
Lacquer paints use organic solvents as their solvent. Organic solvents are NASTY. Lacquer paints smell the worst of the three types of paints. They also damage your body the quickest. One member says that these chemicals are classified in the same class as nerve gas agents. Organic solvents are also what is found in modeling glue, the stuff that melts the plastic between two parts ensuring a good bond. If you're not sure about what lacquer can do to you, get some lacquer thinner from a hardware store and drop a dead fly into it, and see what happens.
That's the bad side of lacquer paints. The good part is, because these organic solvents are so volatile, they also evaporate the quickest of the three paint types, hence they cure the fastest. Also, since they're such a tough bunch of chemicals, the pigment and carrier is also very 'tough' - that is, sticks great to plastic and polishes out well. Won't flake off easily like
acrylic scratch easily like
enamel. Goes on in thin coats, which is great at preserving detail.
Tamiya spray paints, Duplicolor spray paints, Plastikote spray paints, Gunze Sangyo Mr. Color, these are all lacquer paints. Lacquer thinner is used to thin lacquer paints - simple, right? Lacquer thinners can be any of the following: Paint manufacturer's thinner (Mr. Color Thinner, for example), hardware store lacquer thinner, Xylene, Toluene, Methyl Ethyl Ketone (white spirits for UK people), acetone, among others. Acetone is probably the nastiest of the above. It can probably even melt most lacquer primers.
Which brings me to another point: YOU MUST USE A SUITABLE PRIMER UNDERNEATH LACQUER PAINTS! By suitable primer, I mean a lacquer primer. Remember above how I stated the solvents in lacquer paints are the same solvents used in modeling glue? Spray too much lacquer paint onto a model, and it will melt your model. Literally. A good lacquer primer will prevent this, because the carrier and pigment of the primer is strong enough to not be melted by the lacquer paint. The paint manufacturers designed it like this. So, Tamiya primer, Duplicolor primer, Plastikote primer, Gunze Sangyo Mr. Surfacer, any 'lacquer' primer is suitable. The lacquer primer itself usually isn't harmful enough to melt the plastic. Just to be sure, mist it.
Enamel
Enamel paints are some what, in my opinion, outdated. The solvent they use - mineral spirits and petroleum distillates - takes a LONG time to evaporate and cure out. They also tend to go on extremely thick and run easily - that is, paint drops start sliding down the model screwing up your paint job. They take weeks, even months to cure and gas out completely, and even then remain relatively soft when compared to lacquer paints. But they do polish out well when cured.
The good part is that they aren't very volatile. Petroleum doesn't harm plastic. Testors makes a lot of colors in
enamel. They do rock for brush painting though, since they're thicker and take longer to dry than acrylics and lacquers, it gives you a lot more time to play with it and get it just 'right'. They tend to go where your brush goes, unlike acrylics which run all over the place and dry unevenly!
Enamel paints are thinned with mineral spirits and the above mentioned lacquer thinners, besides the paint manufacturer's recommended thinner.
Enamel paints include Testors, Testors Model Masters, and Humbrol. Tamiya also makes
enamel paint that is sold in Asia only.
Acrylic
The best paint, in my opinion, for any type of work except body work. They can be described as 'water-soluble' as in able to be thinner by water, but for the most part, plain old rubbing alcohol or isopropyl alcohol which is its real name is the solvent. There are many advantages to them. One, isopropyl alcohol isn't very dangerous. Heck, if you buy some rubbing alcohol from the store, the bottle says you can rub it onto muscle aches to relieve pain. Two, it dries very quickly. Pour some rubbing alcohol onto your hand and see how fast it evaporates. Feel that cooling sensation? That's cause it's also taking away body heat - like sweat - by evaporating. Just FYI...
Two, they dry very quickly. It's like lacquer paint but without all the dangerous effects. After application, parts painted with acrylics can be carefully handled after just a few hours. Be careful of getting fingerprints onto it, it's dry to the touch but still very soft.
Three, they're easy to clean when using with an airbrush. Windex, rubbing alcohol, heck even water can clean an
airbrush nicely after airbrushing with acrylics.
The bad part about acrylics is that they don't polish very well in most cases. The acrylic pigment and carrier time take a long time to cross-link, and they don't stick very well to the model. Generally if you're painting a car with acrylic color, paint over it with an
enamel or
lacquer based clearcoat, to
polish it out best.
Clearcoat - What are they? Why might I use it?
Clearcoats are paints without any pigments. That is all. The purpose of a clearcoat is multifold. First, it provides a neat little barrier in the polishing process. The single biggest problem in polishing paint is when you polish THROUGH the paint and to the primer or plastic. When you have a clearcoat over the color coat, you're polishing the clearcoat, not the color coat, thus you can use the clearcoat to gauge your polishing process. Second, some people like to 'seal' in their decals with it. Yes, you can paint over decals, but be very careful, as the solvents in clearcoats can melt the decals! Third, with metallic, mica, and pearl paints, you can't polish the paint directly, because this screws up the metal flakes or mica/pearl particles. You see, they don't polish evenly, which is why you must clearcoat over them and polish the clearcoat.
L-E-A
Lacquers,
enamel,
acrylic - this describes the order in which different types of paint can be applied over. What this means is, lacquer paints can have
enamel and
acrylics applied over it,
enamels can have
acrylics applied over it but not
lacquer, and
acrylics can have nothing applied over them. Conversely you can't apply
lacquer over
enamels or
acrylics.
Acrylics over
Enamel over
Lacquer. When you think about it, it makes sense -
lacquer solvents can melt
enamels or
acrylics, but
enamel solvents can't melt
lacquer based carriers/pigments, and
acrylic solvents can't melt
enamel or
lacquer carriers/pigments.
You can get around this through misting, mentioned above. Also, I have found in my experience you CAN paint
enamel over
acrylics, since the two solvents are completely unrelated. But, your mileage may vary.
- source from scalewiki.com
