Shuck oysters, reserving 1/4 cup oyster liquid. Set oysters aside in a small bowl; set oyster liquid aside in another small bowl.
Melt butter in a large saucepan over medium-high heat. Add onions; sauté 1 minute. Add reserved oyster liquid, parsley, thyme, red pepper, and clam juice; bring to a boil. Reduce heat, and simmer, uncovered, for 10 minutes.
Place flour in a medium bowl; gradually add milk, stirring with a whisk until well blended. Stir flour mixture and half-and-half into pan; cook over medium heat 8 minutes or until thickened, stirring constantly. Stir in oysters and artichokes; cook 3 minutes or until edges of oysters curl. Stir in salt and black pepper.