Recently I have been doing some research into how to screen print with cocoa butter to either make custom transfer sheets or to print directly on chocolate. Let me tell you, I have found that although alot of people seem to be doing this already, there is still much confusion about the subject. Equipment can run from the very simple to quite complex. Even if you can get the equipment side right, getting the cocoa butter to be the proper temperature and consistency is a science unto itself.
First, a screen printing, aka silk screening, primer:
A piece of mesh is installed into an frame, together called a screen. The mesh is then coated with a photosensitive emulsion and let to dry. A black and white image is prepared, printed on a transparency, which is then taped onto the coated mesh. The screen is then exposed to light for a certain period of time. Everything that is exposed to the light, ie everything but the black parts of the image, will cure. The transparency is removed, then the mesh is washed. The emulsion under the black parts of the image will wash out, leaving a stencil of the image on the mesh.
If you want a multiple color image, a screen will need to be made for each separate color. You will have to make your graphics for each part. To make sure it all lines up in the end, registration marks are used.
To use the screen, the chocolate piece or acetate transfer sheet is put under the screen. The "ink" or cocoa butter mixture is poured on top of the image and dragged across the screen using a rigid squeegee. The cocoa butter will fall through the screen depositing the cooca butter in the exact shape of the image.
Ok..so how do you get the supplies to do all this and how much does it cost? Well, there are many equipment options. First, the simple route might be to have someone make the screens for you. Chef Rubber can have these made for you; however, the price listed is around $180. If you want to save some money, you can try to make the screens yourself. There are many places to buy silk screens on the Internet or maybe at a local art supply house for less than $30. If you are going to buy pretreated screens or are going to coat them yourself, make sure that the emulsion/diazo is non-toxic. Someone in a different chocolate thread wrote that Ulano TZ/CL is non-toxic. It can be purchased for around $30 and used to make multiple screens. Caution: I don't know of any emulsion which is approved by the FDA. There seems to be some concern around this issue; however, I have been told that the emulsion is safe when dry. I don't know. People are doing it, so you be the judge.
To use the screens, you can either lay them flat over the acetate or chocolate piece and go for it. You could also purchase a screen printing apparatus that holds the frame in place. This is the best option for lining the image up consistently. You can buy one color system for $100 - $200. They also sell systems that can do as much as 6 different colors. These cost over $1,000.
A cheaper alternative I have found is a toy called Silk Screen Factory by Alex Toys. The Silk Screen Factory is neat, but instead of using the photosensitive emulsion, it uses stencils. It only costs $25.
Stencils are an interesting alternative around the food safety issue. Acetate, the plastic used for commercial transfer sheets, can be cut with knives or can be laser cut. You could find a local sign maker or awards place that has a laser. If a stencil could be put on a mesh screen tight enough to ensure that the cocoa butter does not leak, I think this would be the most food safe route.
The most expensive option for commercial purposes is to buy a semi-automatic screen printing machine. Two companies that I have been talking to are Deco Tech and Systematic Automation. According to Deco Tech, you can only use their system to print transfer sheets. Systematic Automation says that their system can be used to make transfer sheets or print on chocolate. I have been told that these systems use a heated screen to keep the cocoa butter at the proper temperature. Cost is several thousands of dollars.
Whatever option you choose, you will have to play around with the cocoa butter and colorants to get the proper mix. It seems that most people advocate the use of powdered colors and titanium dioxide. It appears that many have difficulty getting the color on the cocoa butter to be bright enough once it on the chocolate.
If anybody has experience, please share. Your insight would be greatly appreciated.