For most of these supplies, you will need to go to a traditional art supply store, like Utrecht or Dick Blick or whatever you have in your town. To paint with watercolors you need paint, paper, brushes and a bag full of miscellaneous supplies.
PAINT Do not skimp on paint. Every semester at least one student will walk in with a box of Reeve paints that come in a box of a dozen or so tubes and if they still have the receipt I tell them to just bring it back to the store. They are awful and you will not be able to paint a convincing portrait with them. It is tempting to skimp on paint but trying to use low quality paint the consistency of toothpaste is like cooking with food that isn't fresh. You have to start with good ingredients to get good results. The best brands are Winsor Newton and Holbein (my favorite) Dick Blick also has its own brand which I think offers a nice alternative at a lower price point without sacrificing quality. To save money you can buy the 5ml sizes. I also do not recommend paint by Daniel Smith. They dry out way too quickly. To paint flesh tones and hair color you should have:
brown madder
burnt sienna
cadmium red
cadmium yellow
cerulean blue
cobalt blue
Indian red
Lemon yellow (useful for painting blond hair)
raw sienna
raw umber
rose madder ( or permanent rose or quinacridone rose)
Sap green
scarlet lake
Sepia
ultramarine blue
yellow ochre
These additional colors you will most likely need for painting other stuff in the background of your portraits…
phthalo green (also called Winsor green) a must have color for all watercolorists, in my humble opinion and then maybe these…
phthalo blue (also called Winsor blue)
Winsor red
quinacridone gold
cobalt turquoise
cobalt violet
viridian green
PAPER The only paper I paint portraits on is Arches cold pressed paper 140lb weight which I buy by the sheet. When ordering online they will probably require you to buy a pack
of paper, so this one you may just want to buy 1-3 sheets from your local art supply store.
BRUSHES Sometimes, I use Kolinsky sable but you can use a DaVinci sable/synthetic blend which I also use most of the time anyway. You will need a number 6, 8, and a 12 pointed round.
PALETTE You need something to keep the paint in. The best is the John Pike Palette which is around $28 on Amazon. There are also cheaper versions of the same thing which are flimsy and I wouldn't waste my money on them.
John pike palette - Amazon.com
MORE ART SUPPLIES
Gator board (optional)
gray kneaded eraser
Here are the supplies you can get at the supermarket or you even have these lying around the house:
plastic quart sized container to hold water (old clean soup takeout container)
small atomizer/spray bottle - most drugstores have this too
no. 2 pencil ( nothing fancy)
kitchen sponge
tissues and paper towels and toilet paper-- the cheap kind that has no added oils
Mr. Clean Magic eraser ( buy at supermarket)
packing tape and a large sheet of masonite OR a staple gun and Gator board OR you can get 18x24” Arches cold pressed watercolor block
Camera Get a digital camera – the $100-$200 kind will do or you can get a lens to clip onto your smart phone. I recommend AUKEY Ora iPhone Camera Lens, 0.55x 120° Wide Angle + 15x Macro Clip-on Cell Phone Camera Lenses Kit for Samsung, Android Smartphones, iPhone