This tutorial covers the topic of creating depth in illustrations using Adobe Illustrator. Personally I refer to this style as Faux 3D. That is, the objects are intended to look three-dimensional; however, aren't necessarily completely accurate with regard to light and shadow.
I've found this technique to be extremely beneficial in giving my illustrations a bit of an edge. This will take roughly an hour depending upon your proficiency with Adobe Illustrator.
You can find the source files in the directory labeled 'source' that came in the files that you downloaded. You may wish to look through them briefly before we begin.
First thing's first, open up the supplied assets. You'll find the object we're going to color in a file called "IMPOSTER_OBJECT.EPS" located in the 'source' files. Once you've opened this in Illustrator, grab the swatch library I've supplied to assist in coloring the object. Obviously, if you'd like to choose your own colors bypass this step completely. To import a swatch go to Window in the top bar and select Swatch Libraries > Other Library to locate the file.
Take a minute to familiarize yourself with the object and the layers that it is comprised of.
Now, create a new layer, then add an object that you can use as a guide for the light source. Despite this being 'Faux 3D,' I always find this step useful so things aren't completely out of whack.
This guide helps with defining how to color your shapes and where the highlights and shadows should be designated. Consider this light source guide a sun and use it to gauge how to apply gradients. In this instance I simply created a circle on a separate layer in the top left corner and locked it.
Let's start coloring. Please note that the uncolored shape that you see is white with a black stroke. Be sure to remove the stroke from the object as you proceed with coloring, as it is unnecessary unless desired. Within the bottom edge layer you'll find the bottom face of the object. In the color swatch library find the gradient "OBJECT_BASEBOTTOM."
Select the shape and then this swatch. Select the gradient tool from the left toolbar or by pressing (G) on your keyboard. Based on the light source I have set up, I apply the linear gradient at an angle. Do this by clicking and dragging for however long you'd like the gradient to span. Make sure that the light part of the gradient is the one which is closest to the light source. Repeat this same step by applying it to the shape in the "INNER BASE SHAPE" layer.
Using the same aforementioned technique of gradients based upon the light source, color the shapes within the base layer using "OBJECT_BASE" in the swatch library. Be careful not to color the thin trim, as this is reserved for the gold swatch. You should be coloring three shapes, the outer, the middle and inner. Refer to the images.
In the process images you'll see I've varied the stretch of the gradient. This is directly relative to the surface area of the object and it's relationship with the light source. Thus the outer most layer is largest and needs a longer gradient. In contrast the inner most is the smallest and needs the least span.
Select the middle sized shape on the layer you just colored; from the top menu apply Effect > Stylize > Inner Glow and tailor it to the pictured specifications. We want to make this middle layer look as if it's slightly deeper in than the outer layer.
Again using the same coloring techniques applied to the base, let's color the trim of the object. Use the "OBJECT_GOLDTRIM" swatch to color the thin lines which run around the outside of the inner, middle and outer layers as shown.
Now, in the "SCREWS" layer you'll find two groups for your convenience. One is a group for the face of the screws and the other is for the wedge where a screwdriver would go. Click on the objects and establish which is which.
Select the faces of the screws and apply the "OBJECT_GOLDTRIM" gradient to it in the same way you colored the trim. Keeping them in a group means they can be easily selected and colored as if they were one piece. Further, this is a more accurate way of coloring this shapes with regard to the light.
Apply this same technique to the spiky shape, which is within the inner layer on the base. This shape can be found in the "HUD" layer.
Within the "SCREWS" layer, select the wedges that you have still have to color. Fill these with the "OBJECT_SCREWANCHOR" swatch from the library.
Now, we're going to color the shapes in the "KNOBS" layer using the "OBJECT_KNOBS" swatch. First color the larger one. This gradient is radial meaning it changes from a point outwards. Have your Gradient Tool selected (G) and drag from the middle of the top left quarter into the middle of the bottom right quarter. This smaller gradient gives a shape more depth.
Use this same method for the bottom knobs. The four knobs are grouped; double-click to enter the group. If you're using a more recent version of Illustration you'll be able to adjust the gradients. To do this, on the dotted gradient line that appears on a shape, taper the gradient with the solid black toggle as shown.
Whilst the knobs are starting to look a bit more 3D, there are a couple more things we can do to help them on their way. First, lets apply an inner glow to the four smaller dials. To do this go to Effect in the top bar and select Stylize > Inner Glow.
After this we'll create a drop shadow for the dials. From Effect in the top bar select Stylize > Drop Shadow and punch in the following values:
The bottom four knobs should be looking relatively 3D now. Let's apply this effect to the top large one. First, the Inner Glow.
And follow this with the same drop shadow values you used for the smaller four.
Still in the knobs layer, you'll notice there's a space next to the larger one where it would slide over. First color the shape using the "OBJECT_BASE" swatch.
In order to make it look like it's a little bit deeper within the surface, we're going to add an Inner Glow. Use the following values.
Now let's move onto the "HUD" layer. All the squares are grouped together so in order to access them, double-click the shape. Using the swatches "HUD_Color 1 — 6" in the library, color the squares as you please. I chose an unconventional method of coloring as I was aiming for a random look.
We want the "HUD" colors to look like they are illuminated from beneath. To do this we are going to create an Inner Glow of white. I have a handy trick to apply an effect to a bunch of objects; Go into the group, select all (Command + A), then whilst holding Shift, click on any one of the "HUD" shapes. This deselects one of them.
Then go to Stylize > Inner Glow and use the following values. Be sure to apply this same effect to the shape you had to deselect. The reason that you can't select all and apply the effect is because Illustrator assumes that you'd like to treat everything as one single object. Thus, in order for it to still treat the objects individually, you either need to do them individually (which would have taken much longer) or select everything but one.
Your object should now be coming together very nicely. There should now be a subtle white glow in the center of your "HUD" shapes. Repeat step 13 for the smaller "HUD" at the top of the object. If you'd simply like to reuse the one you've just created, ALT + drag the grouped "HUD" shapes which creates a duplicate. Then hold Shift while scaling it down to match the size of the smaller top "HUD."
We're nearly there. Now to color the shapes in the "EYE" layer. First, select the outer most shape on the layer and color it with "OBJECT_BASE" using the familiar gradient angle.
The next shape in is the gold trim; use the "OBJECT_GOLDTRIM" to color this. Once this has done we need to create some depth for these shapes. Select the outer most layer (which you just colored with "OBJECT_BASE") and apply a drop shadow effect. This is done via Effect in the top bar Stylize > Drop Shadow. Use the following values.
Stay in the "EYE" layer and color the eyeball. Use the "OBJECT_EYE" gradient from the swatch library. It is a radial gradient and thus color it in the same way you colored the larger golden knob; that is from top left quarter to bottom right quarter, yet staying within the shape.
Then color the base of the pupil using "HUD_Color5." In the final piece I used black instead of this, but this decision is at your discretion. For the iris (colorful part of the eye) I used "HUD_Color6."
Next, select the two white circles representing the reflection of the light on the eyeball. With the shapes selected, go to Effect > Blur > Gaussian Blur and use the following values. This creates a blurry shine rather than a hard edge.
Still in the eye, color the veins using "HUD_Color2." Drop the Opacity to 50% so they aren't as pronounced.
One of the final stages is enhancing the shadow over the "HUD" as currently it appears a little too flat. Create a layer above the "HUD" layer but below the "EYE" layer. Then create an ellipse that exactly matches the dimensions of the "HUD" shape as pictured.
Once this is done, fill the ellipse with "OBJECT_SHADOWOVERLAY" and adjust the blending mode to Multiply in the Transparency panel. Also, drop the Opacity to 70%. Again, using the same method used previously for radial gradients, tweak the gradient so the shadow lies in the bottom right quarter.
Finally we're going to give the "HUD" a bit of a sheen. In a new layer above the Shadows, create some ellipses in the top left quarter as pictured. Select the shapes and then choose Effect > Blur > Gaussian Blur and use the below values.
And you're done!
These techniques can be used in larger works. Below is the final project this object was used in.