What is the best way to electronically create halftone positives for sandcarving?

There are some basic rules that apply regardless of the equipment you use. The best way to begin is by performing some tests to determine which input resolution will give you the best results. This varies with your individual scanner and output device.

Even though your output is going to be 35-45 lines per inch (LPI), you do not want to scan your original image at that resolution. A lot of detail will be lost if you scan at such a low resolution. Photos should be scanned at a resolution of at least 200-300 dots per inch (DPI).

Another question people often ask about halftones is: Should we scan our original color photos as color or as black and white? This depends on whether or not you are going to do any alterations to the photo, such as creating a mask around the image area and removing the background. Oftentimes people request that the background be removed on photos of people. Removing the background seems to be easier when photos are scanned in color because you are differentiating between colors rather than shades of gray. Once the background is taken out, you can change the electronic file from color to grayscale. 

Finally, the halftone needs to be output. Halftones should be output at 35-45 LPI. Just as there are many different scanners and computers, there are also many different output devices. Ultimately, halftone positives should be created using AccuBlack inkjet film (or similar brand) or genuine film positives as opposed to drafting film or vellum. Drafting films or vellums simply cannot hold adequate resolution or density. This causes dots to be lost during development because there is a need to wash the film longer to accomplish complete washout in all areas.

Basically, creating halftones requires some testing and patience. However, once you have found what works best, you will enjoy the possibilities of using halftones for sandcarving.

   —IKONICS Imaging