Wood Uniformity

Wood is not uniform throughout, and contains area of different density. More dense area will be difficult to burn whereas lighter area will burn easily. This creates unevenness in the artwork. While it can be beautiful and give character to your piece, it makes dithering extremely difficult. Gradient of grey is very subtile, and a slight variation in wood density will compromise its result.

Below example is from cheap spruce plywood. Note all the veines / glue running through it, and how it was not burned. The lasing was uniform throughout. Stronger power or slower speed will burn through those veines, but will over burn dark area.

Wood veines in spruce plywood

Wood with a lot of veines, different density, or with glue such as plywood, should be used only for pure black / white engraving. Any dithering effect will be difficult to achieve and most photo will not render properly. Fine details will also be lost.

Difference in wood types

From own experience, the bellow are what I personally tried and observed:

  • Cheap Spruce Plywood. This was the worst, very uneven due to glue and wood vein. It also had to be sanded and processed extensively prior to engraving. Best use: Large print without fine details, such as logo or signs.
  • Higher grade Plywood. Finished plywood was a good option. Still uneven, but a lot less, and gave a good wood finish to the product. Best use: Medium to large print, including fine details. Pure Bitmap drawing should be used.
  • Birch Slab. Birch Slab gave good gradient and was relatively even. Some area were denser and other lighter, but overall gave good result. Best use: Small print, including fine details and dithered image.
  • MDF. MDF gave the best uniformity. It can do excellent gradient and is easy to work with. It doesn’t have a nice wood finish, and is more similar to a canvas. Best use: Small dithered image with high details. Note that burning MDF produces toxic vapor.

Update

After further experimentation, cheap plywood can produce very good greyscale pictures. The secret is to condition the wood with Baking Soda (see method here).

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