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Gradients - How to Design Them for Mosaics

womans fingers placing tesserae in a gradient

We produced a video about making gradients that are a key to making the illusion of the third dimension which is essential to 2D art. But, how do you determine the mix of the colors and how the mix changes on each row of the gradient? This is the how.

So let's assume we want to make a gradient that represents a blue sky. It is lightest at the horizon and darkest overhead. We pick a couple shades of blue.

Here is the concept that all the rest of this is developed from. We are going to start with at least 1 solid row of a light blue color and end with at least 1 solid row of the dark blue color. For the in-between, you gradually add more and more tesserae of the finishing color.

The graphic below depicts the starting thought.

grid with top and bottom rows of a gradient

To make a measured change in the color mix. Here are some simple steps.

Step 1 – figure out these 2 things about the gradient (the sky in this case). (1) What are its dimensions (height & width)? (2) How many rows of tesserae are used to make the gradient? As a rule of thumb, more is better.

To answer the dimension question, simply measure the area it will occupy on your backer. For our sky let's say it is 10" high and 20" wide. The horizon is along the 20" dimension so the gradient will span the 10" dimension.

Now that we know that, we can answer the second question – how many rows of tesserae will we use to make the gradient? It depends on the size of the tesserae that will make the sky. Let's assume that the tesserae is 3/8" square, we simply divide 10" by 0.375" (3/8"). The answer is 26.7, so let's round it to 27.

Step 2 – Figure out the rate at which the mix changes. We will express it as a percent. To do that, divide 1 by the number of rows in the gradient and move the decimal 2 places to the left. In this case 1 divided by 27 is 3.7%. What that means is that each new row of the gradient will get 3.7% more of the finishing color. Remember the first row is only the starting color. So the second row will be 3.7% the finishing color and 96.3% the starting color. But, how many tesserae is that?

Step 3 – Figure out how many tesserae are in the width of the sky. We said the sky is 20" wide, so if we divide 20" by 3/8" we learn that it is 53.3 which we can round to 53. The sky is 53 tesserae wide.

Step 4 – Convert the rate of change in the mix from % to tesserae. For that just multiply the 53 tesserae width by 3.7% and the rate of change is 1.96 or 2 tesserae. What that means is that each new row gets 2 more of the finishing color.

The first row is all starting color. The second row gets 51 starting color and 2 finishing color (placed at a random location on the row). The third row gets 4 finishing color. The fourth row gets 6 finishing color, and so on.

grid with top and bottom rows of a gradient

By doing this the middle row (13 or 14) will be mixed about half and half and the last row should be 100% finishing color.

The video mentioned above that demonstrates this can be seen here.

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