First off resin is really messy so make sure you work on wax paper,this is the best to work on it wont stick to it. In this photo I'm just using some scrap box paper. mold ashtray resin
I have found that EasyCast is the best resin to work with it doesn't take too long to dry and doesn't smell so bad, but take a look at the bottles before you buy them, the harder likes to turn an ugly colour or yellow, I find that doesn't matter if you are adding pigment to your resin but if you want it to be as clear as you can get it, you want to take a look at the bottle.
Adding pigments I have tried so many different things to add colour and I have found some things that work the best. If you don't want to spend any money and have some soft pastels around they work really well, all you have to do is flake off a little at a time into the resin NOT WITH THE HARDER! the colour wont take if you have the harder added already. Once you are happy with the colour then add your harder. The best pigments to use is the colours made for the resin you are using, I really mean it you will not get as much bubbles trust me.
You can also add other things to resin as well like sprinkles and sparkles or even candy just make sure you add enough to the resin till it is all full of the sprinkles or it will settle when it drys and you will have a gap of just the clear resin which looks a little silly. One other tip with adding lets say a round candy to your mold, add some clear resin to the mold first and let that dry, then add your candy and then the rest of the resin, if you don't and just add the candy then all the resin at once then the candy will sink and may stick out of the resin when it dry.
When mixing the resin always make sure you mix slow this will help with not having so many bubbles. once you have mixed it 2 times its time to pore it into a mold. The only thing that resin will not stick to is silicone so if you can get your hands on a silicone mold it will be really helpful. You can uses others and buy mold release, I don't find that this spray works for me so I just use a very thin layer of Vaseline works just as well.
Again with poring you want to be slow so you don't get bubbles. If you do see some in your mold just use a tooth pick to pop them. Now time to set your resin aside.
Now the next thing you want to do is sometimes if you don't pore enough resin in your mold there will be a little lip on the back of your object. The easy way to fix this is just pore a little bit of resin on the back to make everything flat, also a good tip is if you are going to add a ring base or any findings to it the best time would be now resin is the best glue to stick anything to it a lot better then glue out there.
Once the resin on the back is dry flip it over, if you are using a silicone mold the only down side is your object will not look clear.Once again the easy fix is more resin. just add a little all round the object like you see here.
I hope my tips has been helpful. Thank you