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Old 11-10-2016, 20:26   #1
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Measuring drops of color for gelcoat

What is the best way to measure coloring for gelcoat? I'm working with polyester gelcoat

I experimented and found that about 4 drops of yellow for each fl oz of white gelcoat is a match for the interior gelcoat.

However, my drops were crude because the cheap pipette I used to measure the drops were not very good and the size of drops varied a great deal.

I'd like to get this ratio as accurate as possible so I can produce consistent color from batch to batch.

What is the best way to measure out the amount of color? If it's by weight, does anyone have a recommendation for a scale and should it measure to the 0.01 gram or is 0.1 gram accuracy good adequate?

Not sure how much gelcoat I'll be mixing at once, but likely in the 2 to 6 fl.oz. range.

Thanks
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Old 11-10-2016, 20:39   #2
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Re: Measuring drops of color for gelcoat

A jewelers scale will get the accuracy yout are looking for. A pocket jewelers scale can be pretty cheap. About 15.00 to 20.00 bucks. Get the calibration weight too. Coins work in a pinch but use new coins. Google the various coil wieghts.
You should be able to get a jewelers scale on Amazon.
You will probably have to experiment again with drops and the scale. But once known you can just scale by percentage.
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Old 11-10-2016, 20:56   #3
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Re: Measuring drops of color for gelcoat

I use small syringes to measure color/tint. It's the easiest way to reproduce the small amount of liquid repeatedly. For instance, 20oz of paint with 4 cc of tint. Different syringes have different measurements, some may be in ounces or millilitre instead of cc.
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Old 11-10-2016, 21:16   #4
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Re: Measuring drops of color for gelcoat

Syringe. Or maybe a graduated pipette.
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Old 11-10-2016, 21:50   #5
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Re: Measuring drops of color for gelcoat

Thanks,

I'll try a syringe. The pipettes I used were to weak to suck the thick tint up and there was a lot of waste and stringy tint between drops.

The tint is pretty thick, do y'all thin it any to make it less viscous or would that add too much variability.

I'll look for a jewelers scale and test that out also. I thought the color matching (spit and cellophane) would be the hardest part, but that turned out to be easy. Getting accurate/ repeatable amount of tint seems to be much harder in small quantities (1-4 ounce total gelcoat).

Anyway, thanks for those dispensing tips.
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Old 11-10-2016, 22:09   #6
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Re: Measuring drops of color for gelcoat

Like the above posters, I used syringes for the colour. Syringes are (here in Oz) in 1, 3, 5, 10 ml and larger. The larger sizes ( ie 20 ml and above) do not provide accuracy anymore I found, although still good enough for measuring and adding hardener! Syringes are quite cheap if you buy the non-sterile ones (ie from pet-shop or agricultural store). And you can even put a cap on the top of some syringes, for later use.

If one were to use scales for the colour, then one have to absolutely be sure to get all the colour out of the (small) container and off the rubber scraper/spatula and into the resin. Or another (better) way of doing it is add colour to a large container, weigh that and then add the (gelcoat) resin after that. However one might lose some accuracy with this method.
I guess, using a scale for the colour, an accuracy of 0.1 gram is good enough, but one may get away with a 1 g accuracy, depending on the quantities you work with (the larger the quantities that are mixed, the need for accuracy becomes less important).

It is nearly as important that the volume/weight of the resin is accurate. I used a digital scale for that with 1 g accuracy. A scale for up to 2 kg (~4-5 lbs) would take take of all small jobs.
Happy gelcoating!

BTW, colour matching I found extremely hard, and I seen very few people who can do that well.
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Old 12-10-2016, 10:34   #7
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Re: Measuring drops of color for gelcoat

Can you estimate the entire amount of gel coat you will need and tint the entire amount at one time?
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Old 12-10-2016, 12:35   #8
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Re: Measuring drops of color for gelcoat

Always mix way more than you think you will need. Store left over in a container just the right size and seal tightly.

The trouble with mixing repeatability is the minuscule amount of very concentrated pigment for small batches of gelcoat. Never add pigment directly to the batch, or you will surely "f" it up. One trick is to dilute the pigment 1 mL per 30 mL of gelcoat base. Makes it much easier to tweak the colour without accidentally adding too much.

Attempting precise measure really isn't with it as the boat will be 50 shades of grey (or whatever colour) from top to bottom.
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Old 12-10-2016, 12:39   #9
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Re: Measuring drops of color for gelcoat

Quote:
Originally Posted by ramblinrod View Post
Always mix way more than you think you will need. Store left over in a container just the right size and seal tightly.

The trouble with mixing repeatability is the minuscule amount of very concentrated pigment for small batches of gelcoat. Never add pigment directly to the batch, or you will surely "f" it up. One trick is to dilute the pigment 1 mL per 30 mL of gelcoat base. Makes it much easier to tweak the colour without accidentally adding too much.

Attempting precise measure really isn't with it as the boat will be 50 shades of grey (or whatever colour) from top to bottom.
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