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Erasing Cortex Seam Lines: DON'T DO IT

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Posted (edited)

First of all, I need to make some disclaimers.

I do not own nor ever will own a Smart Doll Cortex.

My hobby background consists of building plastic model kits and I have quite a bit of experience with them. This background has helped me make a number of suggestions at the Care and Repairs section of the forums. Despite my background, I will make no claim I am an expert at eliminating seam lines. I will, however, make the claim I am an expert at having FAILED at it. Because I have failed, I can say the things below.

Having said all that, allow me to discourage you from erasing the seam lines on your Cortex doll.

Part 1: Sandpaper Only

If you're *ONLY* using sandpaper, you'll make the seam lines harder to see but they'll still be visible. Light will also reflect on the sanded areas differently than on non-sanded areas. Whether you want to sand down everything using fine grit sandpaper will be up to you and how much you're bothered by the different reflections.

Part 2: Plastic Model Cement Method

Another option is to apply a slight (and not extreme) excess of plastic model cement on both pieces you're trying to glue together. Apply the cement, let the cement "overflow" from the seams of the parts you're combining, wait for the cement to dry completely, and then use sandpaper to sand off the hardened overflow.

In theory, this method works wonders. The cement slightly melts and fuses the pieces together. When you sand off the hardened overflow, the seams would have been filled with melted plastic in the same color as the pieces you're combining.

In practice, the ugly problem coming out from this method is unfixable (without using the methods in part 3). When you use a coarse enough sandpaper to sand down the hardened excess, you won't always be able to sand down the excess cleanly. You'll inevitably remove more than you want, which will result in pot holes across the seam(s). There can be a number of reasons for this - the cement didn't dry hard enough, there were small air pockets in the cement, whatever - but the reasons don't matter. You'll be left with pot holes on the pieces you fused and you'll have little to no ability to fix this problem.

Part 3: Filling, Sanding, Painting Method

The traditional way to get rid of seam lines on a plastic model kit is to cover up the seam lines with putty, wait for the putty to dry, and then sand down the putty.

The best putty for the Cortex is the kind you could make by using the runners ("trees", "sprues") the parts were cut out from. If you were to take the runner, cut it into tiny pieces, and then shove them into a bottle of liquid plastic model cement, you can create putty specifically for Cortex. You can even adjust the consistency of the putty by adding more runner pieces or glue. If you end up with "pot holes", you'll have the correct color putty to fill in such pot holes. However, that's assuming your Cortex doll included those runners. If you don't have the runners, you're SOL.

So you don't have access to the runners your Cortex doll was cut from. Now what? Time to use *some* putty. The color of the putty you use will not match the doll's skin tone. After eliminating seam lines, you'll need to paint the entire body. This means you'll need to mix your own paints because if you buy any over the counter "flesh tone" paint from a hobby retailer, that color will not come close to matching the doll's skin tone. You won't need to mix paints if you plan to paint the head as well. However, if the head already has a faceup on it and you want to keep that, you'll spend quite a bit of time trying to mix the correct color. If your doll has a "Tea" or "Cocoa" flesh tone, you'll see the difficulty of mixing the correct color paints jump.

Part 4: The Aftermath

So let's say you successfully eliminated the seam lines. If any of the doll's joints need to be adjusted for any reason, how are you going to do that? You'll have to disassemble your doll. In order to disassemble your Cortex doll, you'll need to...

I don't think I need to finish that previous sentence.

I didn't even get into the issues of paint chipping. Even with paint chipping, I think that's the least of your worries.

If after all this you believe I am wrong, then don't let me stop you from eliminating seam lines on your Smart Doll Cortex.

For everyone else, a Smart Doll is an expensive hobby item to destroy. Don't try to eliminate the seam lines. Don't ask your friend who builds Gundam kits to eliminate the seam lines. Leave your Smart Doll alone. If you don't like the seam lines, cover her up in clothing which minimizes their appearance. You'll be much happier not destroying your doll.

Edited by growcian
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The more I learn about Cortex, the more I am glad for my vinyl girls. I can see why Cortex would be great for some people, but those seam lines would bother me. I'm a little perlexed as to why it's been mentioned by Danny that Cortex will change everything and blow us all away (don't ask for me a direct quote, because I cannot remember where I saw that but probably on Instagram).


Knowing nothing about Gundam kits, I briefly entertained the idea of doing just that--learning how to erase the seam lines if I ever got a Cortex. I thank you for your post, because I really would have had no idea. I agree as well as I wouldn't experiment with such an expensive hobby item. You listed a lot of things that I would have never even considered!


I wonder since in the end the heads won't be vinyl how easy/difficult it would be to mess up the face paint on a Cortex girl.

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Cortex is a great option for people who are too uptight about possibly getting stains while playing with their lovely dolls. (No offense, I used to be one of them.) The seamlines aren't that ugly to me, perhaps because I'm used to resin. Trying to get rid of them kind of defeats the purpose, you're better off getting a vinyl then. I wouldn't however get a cortex just for the price difference. I find it negligible. 

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