The Blend Tool has a Spine!

If you have ever used the blend tool to blend objects or create a slip shadow, did you know you can control the spine along which it blends? You can even replace the spine with another line or object! Check it out, it's quite interesting. 

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Start with text or any shape. I used a letter to show this example. 

Outline the type. Choose Type>Create Outlines. Fill it with a color and set this one aside for use a few steps later.

Duplicate the shape and add a fill color. Duplicate the shape again and add a different fill color. 

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Select both shapes and choose Object>Blend>Blend Options. From the Spacing options menu, choose Smooth Color. This just sets the options. 

To make the objects blend together, choose Object> Blend> Make. This will blend the shapes/colors together. Notice how the darker color is behind and blends to the front, lighter color.

Select the shapes and you will see a connector line (a spine) that connects the two shapes and creates the blend. 

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Choose Object>Blend Options and choose Reverse Spine Front to Back to control the start and stop order. 

This reverses the Front to Back order making the Blend look like it is going from dark to light. 

Go to Outline mode under the View menu to see the two object that blend together and the spine connecting them together. 

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To edit the spine, use the Curvature Tool to click on a point of the Spine and move the point. 

Go to View>Preview to switch from Outline mode to Preview mode and see the Blend results. (The original shape I copied and set aside I moved on top of the start of the blend to see the shape better, it is not part of the blend.) 

Use the Curvature Tool to change the spine curve or change the start and stop points. 

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Any editing of the spin will be reflected in the blend of the objects

If you want to change out the spine, draw a new line of or closed shape. The spine will be invisible so no need to make it a color. 

Select the new line or shape and select the blended object and choose Object>Blend> Replace Spine and the new blend will blend along the new spine.