You can make an earthenware slip. As for pros and cons I find earthenware to be far too messy in any application.
I just hate that it stains everything and it will probably stain your mold.
Though the benefit of it over earthenware is it usually has a low vitrification which means that it becomes more waterproof at lower temperature due to iron content.
So yeah, it’ll be safe either way.
The only time it could be potentially “Dangerous” is if there is a non-food safe glaze in your studio, which is doubtful but it’s always good to check.
You don’t want poisons leaching into your food.
Also, just for future reference for vessels and glazes: Make sure the glaze fits your clay body. Crazing can be a nice effect but can make it impossible to clean. The same goes for crawling glazes. To be fair I am drinking out of a coffee cup with a shino glaze inside, and I am still alive!
I’ve made molds a thousand times but still forget things.
I would make a mold with four to six pints so you can make them in batches and the thicknesses will all be the same in the batch. Get a big plastic tub to pour the plaster in, to save the trouble of making kottle boards for what is probably going to be a one off for you.
Remember you don’t have to use an actual pint glass – any cylinder could work. So buy cheap plastic cups for your original. If there is printing on the bottom or other marks, you could try sanding them off, or filling them in with clay so you don’t have the manufacturer marks on the bottom.
Wear a respirator and or work outdoors when you mix the plaster. Don’t want the dust getting in the clay studio.