If you are new to pin making and producing physical products in general, please read this. If you've made tons of pins, some information may be enlightening, but overall, this is geared towards first timers. If you make hand made products for a living, none of this information will be shocking.
It's important to set some realistic expectations in regard to actual production on pins. 99% of the time, all is good, but these are the top things people have misconceptions about, especially if you are new to manufacturing products. If you have zero flexibility, pins may not be the best item for you. I'm attempting to give some straight shooting honesty for you to decide if making pins is the right product for you to sell.
Pins are still a 95% handmade item. The master mold is cut by a machine, but every other step in the process is done by people, colored by hand with little eyedroppers of color, etc. The pins will not be a 100% perfect machine pumped out item, so you need to have realistic expectations. This is not meant to scare you, but I see newbies to pins complain about the same few things due to a lack of understanding and ignorance to the process. Any legitimate factory quality issues will always be bought back or replaced with extra for the hassle.
The following things do not merit either of those options.
Pantone colors are mixed up for your job and are made by combining 3-4 different mixing tones, just like if you've ever mixed paints, so although they do their best to mix to the exact pantone, the color can not be guaranteed to be dead on. The tone can shift 1-2 tones and this is part of the process, so we need to be realistic. On lighter tones, 1% more of one of the components can shift it. In 7500 C listed below, it takes 0.6% black and 0.3% Warm Red out of 100, so try to perfectly attain that and you'll understand why there can be slight variation. This also means that a reprint of a pin at a later time may not dead on match the first batch and you have to be ok with that. the inks are water based, so they have a limited shelf life once mixed before they harden, meaning they are mixing the color for your specific order.
The way they are made hard enamel is by applying a ton of pressure and force to the top of the pin against a buffing wheel to flatten them, so the mold line thickness can vary. This is not a controllable variation and is another facet of a hand made item. If the same worker makes all of the pins in the same day, the line thickness of the molds can vary still. If this is a breaker for you, soft enamel is suggested. Hard enamel pins cannot be rushed if you have a shorter than 2.5 week in hand need. There are too many steps in the process to make them, but soft enamel can be rushed if needed.
Glitter is...well, glitter. We've all tried to use it at some point and it's messy. The way glitter is done is by adding actual glitter into the ink and they tend to use the closest match from the image below unless requested other wise. Being that it is a sparkle powder mixed into a liquid ink, it can shift around and group vs being a perfectly even layer. For instance, if you want green glitter in white ink, we can do that. Because the glitter has multiple tones in it and is intended to reflect light in that way, it can make the color look differently than just the pantone. For example, if you are using a red pantone 485 C and some is in regular ink and some is glitter 485 C, they will visually have different tones. This is normal.
Glow in the Dark Ink
Glow in the dark is a powder added into an ink and mixed in. It tends to make the color look more matte because of adding the glow powder in. The lighter the tone it's mixed into, the brighter it will glow because it's glowing against that base tone. So, if it's glow white, it will be much brighter than a dark blue with glow in it. This is simply because trying to glow against a dark base tone is muting it, so it's best used in lighter tones to get the best results. Example below shows multiple shades of green and how their tonal differences effect the overall glow. As you can see, the hands(lightest tone) glows brightest. In bright light, your color will look like it's normal tone, but as the light the person wearing it in shifts, your pin will begin to lightly glow, as it should, so there is no ta-da moment unless someone goes from bright lights to lights out.
Sizing your pin - Print it out at home at size
How do you know what is the best size to make your pin? Some people like smaller pins, some make 2" pins and it's totally up to you and how ok you are with some changes that could be needed based off of your desired size for that design. If you tell me you want something at 1" and the details simply wouldn't work at that size, I will say, what about 1.25" or suggest a detail reduction to see what you prefer. Hands down, the easiest test that barely anyone does is to put your art on a page in your art software at a few sizes and simply print it out at home. There is no better way to see how your pin will feel in real life than really seeing it. 1.5" doesn't mean much on your 17" monitor unless you print your art at 1.5" at home to see if you like it. An easy test of your details and how successful they will be is to hold that print out at arms length (average distance someone will see your pin on another person) and if things start looking muddy, reduce your details. A busy pin always looks like crud.