The first step here is to confirm you can print using the origianal Artisan 50 driver. If that does not work, then something is wrong with your installation (printer is not on, not connected, or something else altogether), contact Epson Support for more help with this.
As of Mac OS 10.9 you need to download drivers to set up your Artisan 50 for PVC card printing.
These drivers are no longer pre-installed, so unfortunately you have to download a rather large file to get them.
Download here: http://support.apple.com/kb/dl1398.
Install the drivers, and restart your computer.
Go to the Apple menu and select "System Preferences…".
Open the "Print & Scan" preferences.
This is the most important part. Even if you already see your Artisan 50 printer (as shown in the image), you must do this to ensure you can print on the entire surface of the Inkjet PVC Card. Select "Add Printer or Scanner…"
Select "EPSON Artisan 50" at the top of the window, then at the bottom where it says "Use:" select "Select Printer Software…".
In the search field at the top type "r280". In the search results select "EPSON SP R280 Series". Do NOT select anything that says "Gutenprint", they will not work properly for Inkjet PVC card printing.
If you don't have the option for "EPSON SP R280 Series" you need to install the Epson R280 printer software. Please see Epson Support for that.
Rename the printer so you don't confuse it with your normal Artisan 50 printer. We named ours "Artisan 50 - PVC Card Printing" to make it very clear. After you enter a new name confirm that the "Use" says "EPSON SP R280 Series", leave "Location" alone, then click on "Add".
After you click "Add" it will confirm that you want to create "another" Artisan 50 printer, click on Continue. You can now select this printer in any application in the Print dialog box.
When printing be sure to set the print settings correctly and to set your printer up properly: