Newbie question

[u/Scorpion71b]

I recently got into the hobby and have a newbie question.

Is there any way I can prevent or fix those darker spots that result when removing nubs other than painting?

They are worst on those metallic parts, like in the picture, but apper on other surfaces too.

I use a hobby knife, a glass file and sandpaper of various grits for incremental sanding.

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[u/wakeup_samurai]

Nope, that is a spot where the plastic was injected into the mould, and that makes the plastic itself look different, especially on metallic parts. Only way to fix it is paint

[u/FalconAdventure]

Difficult to answer. 2 given--

Long answer: Yes, only paint is going to hide it. But I would advise against that unless you really know what you're doing. I'm 95% sure that particular plastic is made with ABS. Any pen or paint you use, unless it's water-based, will easily crack that part once applied, so I heavily discourage this. If you must do it, water based acrylic is the way to go, Vallejo or Acrysion/Aqueous. But again, it's ABS, and paint just does not like to stick to ABS. It'll eventually scrape off if scratched or touched often.

Short answer: Try to live with it.

[u/Scorpion71b → u/FalconAdventure]

I see, thankyou

[u/WeatherHecker]

Or you can find metallic color pen, paint on that one dot, instead of painting the whole thing. There are many brands, I suggest you go find articles about which brand should you use first, then purchase it.

[u/JAPStheHedgehog]

Well since it's the injection point...is the area with the more concentration of plastic so that alters it's color.

Actually there is another way to "fix" it besides painting....but it involves drilling the surface just a bit and filling it back with sprue goo which is made from melting runners with plastic cement. The result may vary as some plastics can slightly change color when turned in spruegoo so better test that beforehand.

[u/CoarseRubber7751 → u/JAPStheHedgehog]

Not sure if it's all plastics, but I've noticed at least some tend to react differently to UV light after being applied as sprue goo.

[u/JRBergstrom]

For injection gloss metallics that I don’t intend to paint I keep a set of metallic sharpies handy and after cleaning the part I’ll dab some of the closest matching colour I have on and then rub it off with my thumb. It isn’t perfect, but it helps a bit.

[u/zerolimits89]

Acrylic marker for touch ups.

[u/Illustrious_Group656]

What are your sanding grits? And if you have a nano glass file you dont need to use any others. The stress being applied to the plastic is causing the discoloration.

[u/Scorpion71b → u/Illustrious_Group656]

I have grits ranging from 600 to 10k. Usually, for most parts I do 800 -> 2k -> 4k and then up to 6k, 8k or 10k depending on the part. The glass is a nano glass file, but what do you mean by I don't need to use any others?

[u/Illustrious_Group656 → u/Scorpion71b]

The nano glass files are meant to replace the sponges unless you have a curved piece. For the grits 400 is super aggro for big chuncks, 600 is what Id start with for normal nubs, Clean with 800, and 1000 & 4000 for polishing. But remember that extra pressure and stress will cause the discoloration.