Why Do Some Model Horses Shrink While Others Do Not?

A collector asked me this recently, and I really went down the rabbit hole in explaining.  I apologize to her... It was probably a much longer email than she was hoping for!  But why do some models "go shrinky" while others of the same release don't?
It comes down to when the model was molded.  That seems overly obvious, but many people don't realize that a model can be molded ten years before it's painted.  That changes the story quite a bit, doesn't it?  
If we think about the production process, Breyer has a factory where they're putting plastic into injection molds to create the whiteware bodies that eventually get painted to become the models we love.  The plastic comes in as pellets, and we've got to expect they're going to get it in BIG batches, since they're doing runs of thousands of each mold at a time.   
We know, for example, that their limited editions are usually around 3000-10,000 pieces, so we can assume those are probably all painted at the same time.  That means they had to have at least that many whiteware bodies ready before painting began, and likely, the high end of that range is a good estimate for how many bodies they may make of a mold at one time.
Breyer is very secretive, so we don't know the actual quantity they make at a time, but let's assume the 10,000 number.  (You'd want to make a large amount, because cleaning the mold tools and changing to different molds takes time and money.)  When they make thousands of bodies (or tens of thousands), they don't necessarily paint them all at once, particularly if a release has been in production for years.  When a release first comes out, it sells a huge amount the first year, and then sales slow down, so even though they still need to ten  thousand at a time to be efficient, maybe they only order 2,000 to be painted and leave the rest as whiteware in the warehouse until they're needed. 
The so-called "Shrinky Era" is generally considered to have occurred starting in the mid 1980s and running into the mid-1990s, but those dates are pretty squishy. 
Using the dapple grey PAS as an example:  He'd been in production since 1972 and continued through 1988.  Most people already had him by the mid-1980s... If they didn't get him new, they may have found one at a flea market or had one passed down to them.  Still, Breyer had to make batches of whiteware bodies when they started to get low, so let's say they made 10,000 PAS bodies in 1984.  He was in production through 1988, which is in the shrinky era, but if they already had whiteware waiting in the warehouse, maybe they didn't make any with the "shrinky" plastic.
Or, maybe the last batch was made of that plastic in 1988, so a thousand or so, made in shrinky plastic, were painted dapple grey before that release was retired.   Then the rest of that batch of whiteware were later painted rose grey for the release that debuted in 1989.... and maybe some were still in the warehouse to paint some of the light dapple grey release that came out in 1991.
There are a few possible scenarios, but I think you get it.  It all depends on when the whiteware was molded, not when the model was painted, and they can wait for paint for years.  Heck, they're still pulling Alborozo whiteware out of the warehouse to use for Breyerfest auction models, and we know that steel molding tool was destroyed in 2008, so they can hold onto whiteware bodies for a long time for future use!
So, that explains why some long-running releases may have both shrinky and non-shrinky individuals.  When a mold debuted during the shrinky era, that's the first time it was molded, so there were no leftover bodies to use.  Therefore, everything made on that mold, from the inaugural date until they changed the plastic mix, is going to be made from plastic prone to shrinking.  
Also, did they source all their plastic pellets from the same place during that time, or could it have been one supplier who had an incorrect mix that they bought from occasionally?  We don't know.  And, since I'm already so deep in this, we DO know that models that are culled from production because of flaws like bad seams, missing parts, etc., get ground up into pellets and added back into the plastic bin to be reused.  Shrinky whiteware that may have been sitting in the warehouse, waiting to be painted, could have been pulled out years later for painting, found to be defective, and ground up, resulting in a mix of "good" and "shrinky" plastic in models molded even after the problem was found and fixed.  It's enough to make your head spin... and it's why we'll never have exact cut-off dates for "The Shrinky Era."
Whether a model shrinks, and how much, is determined mainly by how it's kept.  Models that are wrapped or stored away in fairly airtight containers tend to shrink fast and often get ugly.  Those displayed with good airflow sometimes barely change at all.  Heat is definitely a factor, and perhaps humidity as well, but there's something about being wrapped or packed away that seems to make them degrade.  I have a feeling it has to do with the buildup of gasses inside their hollow body cavity, when it doesn't have a good means of escape to dissipate, but I haven't found any scientist who can give a real explanation.  (And I've tried!  I've contacted chemical engineers, museum plastic conservators and movie film archivists, since they experience the same issues, but so far, they have all seemed to think that studying plastic ponies is not worth their time.) 
"The Shrinky Era" a fascinating part of Breyer history.  Some folks may have seen their first shrinky as a horror image on social media, of a twisted, lumpy, oozing model, and gotten a gut reaction to anything shrinky.  But while some do get ugly, many seem to simply become slightly smaller, adorable versions of themselves, and some collectors seek them out as a delightful addition to their congas. 
I have a few in my personal herd that look like the "little brothers" in the conga line, and I cherish them for their individuality.  I've had some for more than 30 years and have seen nearly no change, as they're displayed on open shelves.  If there's a model I fall in love with, and I find one that's a shrinky in good condition, I won't hesitate adding him or her to my herd, knowing I will be able to care for them and enjoy them for the rest of my lifetime.
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I’m glad you were able to display them safely for 30+ years. I have a few shrinky models that I enjoy & feel reassured by this article.

Mary Walker

You don’t need to apologize. :) This is good information, and something every serious collector should know! Thank you for sharing it.

Coreada Kelly

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