Yep, sure. So a lotion would ideally be a little better. It would prevent evaporation better and the oils and waxes might help the GTE absorb better. This website is a good reference on how to make lotions with basic ingredients. The important ingredients are the oil and beeswax, and the most important step is the heating and mixing. You can modify this recipe basically to include anything. I don't know what the pH is though, for GTE stability the more acidic the better.
I believe the steps they describe are an oil-in-water emuslion. If you want to do exactly like what they did in the Mahmood study, you'll have to create a water-in-oil emuslion. These are much trickier. You'll first want to get an emulsifier with a low HLB value, that'll be the hardest ingredient to obtain. Something like soy lecithin should be okay. If you're not sure what the HLB value is for, and for more info on emulsions, look here.
And if you are looking for something to easily add to the water solution to aid absorption, some type of ethanol/everclear/pure grain alcohol would be ideal. Just a little bit would greatly increase absorption. The problem is putting ethanol on your face may not be a good idea, I really don't know if it would cause problems or not.
And lastly, I'm not sure putting in on while IN the shower is good, but putting it on within 15 minutes of leaving it is what I try to do. Your skin is more moist, you're pores are open, and the heat from the shower may cause your capillaries to dilate. All very good conditions for increased absorption. Women seem to have been born knowing this LOL, the ones I've known almost always put on some kind of lotion or moisturizer on after showering.
Thanks for the info! I think the water-in-oil emulsions might be more hassle than I would want to bother with. As for the oil-in-water emulsions, I do have some jojoba oil already so I would just need some beeswax.
However, after looking at all this, I'm wondering if it would make more sense to simply buy a ready-made green tea cream from the store. I'm curious to hear your thoughts on this. I don't know if you have a reason to think this would be less effective than using a homemade cream.
The serum I'm most interested in after looking around is the SkinActives T-Zone Serum, which appears to have a relatively small number of ingredients:
Distilled Water (Aqua), Lactobacillus/Kelp Ferment Filtrate, Porphyridium Extract, Laminaria japonica Extract, Arthrospira Extract, Azeloyl Glycine, Epigallocatechin Gallate (EGCG, Green Tea, Camellia Sinensis Leaf Extract), Niacinamide (Vitamin B3), Nobiletin, Propylene Glycol, Diazolidinyl Urea, Methylparaben, Propylparaben.
The other products that caught my eye are the Proactiv Green Tea Moisturizer, Alba Botanica Hawaiian Aloe & Green Tea Oil-Free Moisturizer, and Jason Tea Time Moisturizing Creme. I would provide links to these products but I think this site has a rule against linking to product pages.