I’m not yet an acrylic user, but there is something I’m curious about. Maybe Triarius can explain it. I am always reading that people have to add a retarder to acrylics. Why don’t the manufacturers add retarder to begin with? Wouldn’t that give them a sales advantage?
"New Brand XYZ Paint, now with retarder added"
It can’t be that expensive.
Don
The chemicals in retarders are not completely compatible with some of the components of the paint, particularly the binders, and sometimes the pigments. Retarders work by either inhibiting solvent loss, delaying the onset of crosslinking (curing) or both. Most work predominantly by delaying the onset of curing. However as a consequence of this, when a retarded paint starts to cure it cures very rapidly, up to twice as fast as the unretarded paint. That is why you should never add retarder directly to paint (always mix it with solvent, first) and why you should not try to store paint that has a retarder added for more than a day or two.
Thanks Ross. I knew you would know.
Don
Hi Don,
Actually, brands such as Tamiya and Gunze acrylics already contain an amount of glycol, which I believe is the retarding agent.
I’m guessing that the amount already added to the paint is sufficient to meet their basic “performance” specs under controlled (temp, humidity) conditions.
In the real world, sometimes we have to tweak it a little…[:D]
It’s not merely a matter of “glycol,” it’s a matter of which glycol. It appears easier to gain access to top secret CIA documents than to find out what’s actually in Tamiya paint—and Gunze is worse—at least unless you read Japanese.
Golden retarder contains propylene glycol, but obviously contains other materials, as well, from the MSDS (which provide information only on “hazardous” components and are not required to list “proprietary” ingredients). I know that some acrylic polymers are incompatible with various forms of glycol, but not with others. This would seem to indicate that propylene glycol is universally compatible. However, I also know that retarders are only marginally compatible with some of the acrylic polymers used in hobby paints. (Yes, I actually tested this.)
Glycols generally reduce evaporation rates in either alcohol or aqueous systems. However, some also interfere with acrylic polymerization, making them ideal for acrylic systems. There are also other chemicals which interfere with that polymerization, and I suspect they are present in some acrylic retarders, since the result of adding too much retarder (or adding it directly to the paint) is rapid flocculation.
It therefore seems a reasonable assumption that proprietary thinners that contain a retarder contain propylene glycol (possibly with other chemicals), or they contain a different glycol that is compatible with the acrylic polymers in that particular brand.
Please remember: too much retarder=ruined paint.
Phil, how did you find out that Tamiya and Gunze contain glycol? I’ve been trying to dig up that information for years!
This is the first I’ve ever heard of Tamiya or Gunze paints containing retarder, hard to believe with the ultra fast surface drying.
I know that Tamiya’s thinner includes a retarder, but I’m pretty sure the paint doesn’t.
Hi Ross,
In tiny print on the Tamiya label: “Contains Isopropanol and Glycol Ethers”
In even smaller print on the Gunze (aqueous) label: “Ingredient: Acrylic Regin - 23%, Pigment - 14%, Alcohole - 27%, Glycole - 10%, Water - 26%” (Spelling is as per label [:-^])
On one of my older (1980’s vintage) Tamiya jars, it doesn’t mention Glycol, but states:
Component Element:
Water soluble acrylic resin 40.3%
Pigment 14.1%
Alcohol 19.9%
Water 25.7%
This one is from about the time when you could still brush paint Tamiya straight out of the bottle. [sigh]
Holy cow, you can READ that fine print! [8D] <— not “cool” but BLIND!
Equivalent of the Holy Grail?
Couldn’t find one for X-22A Acrylic thinner though - it’s listed, but it’s wrong. They have the enamel thinner listed as acrylic.
If anyone wants to go rooting around a bit further, click here: http://www.google.com/search?hl=en&rls=com.microsoft%3Aen-au%3AIE-ContextMenu&q="Ikegami+Paint+Manufacturing+Sales"%2B"tamiya"&aq=f&oq=&aqi=
I never even use any retarder when I paint. [:-^]
Wow! I checked out a few of their other colors and Propylene glycol runs anywhere from 13 to 17%. Do you still need to add more retarder?
Don
“Ah!” cried Holmes, “We have them, Watson!”
At those amounts, the glycols are not retarders, they are cosolvents. In this case, cosolvents are modifying the behavior of the primary solvent, isopropyl alcohol, probably for viscosity and evaporation rate.
A retarder is generally added in amounts well below 1%.
Hi Don,
I suspect that the requirement for retarder can vary depending on technique and ambient conditions.
For example, I typically airbrush Tamiya acrylics at what most would consider very high dilution (50 to 80%+ thinner), at low pressure and rarely require (additional) retarder.
This is starting to sound like eye of newt and a pinch of henbane. I think I’ll stick with enamels.[:)]
Don
He knows. Now we’ll have to kill him…
[(-D]
Actually, Don, you have no choice. You must use acrylics. Otherwise—Gulag! Seriously, enamels will probably get phased out in the next 5 to 10 years, perhaps sooner, depending on how rapidly the technology develops. There is a lot of push behind that technology! Enamels are a very old technology, in which fundamental change is rare, so they seem less complicated.
Oh, by the way, it’s actually wing of bat, hair of frog, and a pinch of henbane……[}:)]