OCAD Studio: Comparative Measurement

In this lesson I will show you the basic principles of ‘comparative measurement’ – this is a pretty tricky technique, and for a lot of artists it may feel too scientific, so I totally understand if you’d prefer to work in a more instinctive and expressive manner. I personally don’t tend to work this way in my own art, however I do occasionally refer back to the principles when I’m problem solving an issue in my drawings.

  • You’ll need to start with a height for the subject (a mark for the highest and lowest points).
  • Then you will need to figure out how wide the subject is relative to its height.
  • It could be half the height, 1/3rd or 4/5ths.
  • Then match this ratio in your drawing, doing so will ensure that you match the major proportions exactly.
  • Follow this process for the rest of the drawing.
  • Look at the relationship between distances within the subject and then match those relationships in your drawing.
  • It’s all about ratios which can seem very technical but this helps ensure that you are super accurate.

OCAD Studio: How Shadows Work

In this exercise, you will be creating a sphere, but the same principles apply whenever you’re drawing or painting any form in a representational artwork. 

Use the diagram below or watch the accompanying video lesson as a guide when you create your own sphere.

The Form Principle.jpg



  • Paper
  • Pencil or charcoal
  • Eraser


  • Toned canvas or panel
  • White paint
  • Either black paint or
  • An earth colour paint (such as burnt umber or raw umber)
  • 2-3 small to medium sized brushes
  • Odourless mineral spirits
  • Palette
  • Cup for mineral spirits
  • Cleaning rag


Determining the Light Source

1. Draw a circle on the page or canvas, this will be the basis for your sphere. Then draw an ellipse on the ground plane, this will be the shadow cast from the sphere and determine the direction of light.

2. Draw the ‘bedbug line’ (the line that divides light from shadow) onto the form.

Establishing the Shadow

1. Fill in the the shadow shape with an average shadow value (about a 7 on the value scale). 

2. Next, fill in the cast shadow on the ground with a similar value.

Adding Variations to the Shadow

1. The shadow isn’t usually evenly dark, because in most cases, light will be reflected into the shadow after bouncing off other elements in the scene. This will cause the centre of the shadow to lighten, becoming darker towards the bedbug line (the ‘core shadow’).

2. The shadow will also become darker where two forms meet one another (like where the sphere meets the ground). This is called the ‘occlusion shadow’, it is dark because neither direct light or reflected light reaches it.

Adding Halftones and Refining the Form

Begin adding halftones from the bedbug line, these are the ‘dark halftones’. As the halftones move further away from the bedbug line they will receive more light, and begin to lighten as a consequence.

If you are painting on a toned panel, at a certain point you will reach a value that matches the canvas. When this happens you should stop adding dark halftones and start working out from the lightest values. You will find these values at the part of the sphere that faces the light source. Once you’ve added all the lightest halftones, they will meet the darkest halftones.

If you are drawing your sphere you can just keep adding halftones gradually. The further that halftones are from the bedbug line, the lighter they will be. At some point you will just leave the white of the paper.

  • In stronger, direct light, the transition from the bedbug line will be more harsh.
  • In weaker, diffuse light, the transition from the bedbug line will be more gradual and softer.

Now that all the halftones have been added you should have a roughly correct sphere. At this point you should spend time correcting value relationships and neatening up your painting or drawing. 

Task 3 Charcoal

Drawing the universal forms is great practice before taking on more challenging still life drawing. It allows you to learn about how light and shadow work on the main forms for all future drawing. It also gives you chance to experiment with a new media…in this case, charcoal.

You are aiming to produce each of the main forms: Cube, Cylinder, Sphere and Cone, using your charcoal media.

To get a richer experience, do try to leave the confines of a sketchbook. Larger pieces of paper work very well and allow for different expression of markings. Being able to smudge easily, you will find covering large papers much easier than with graphite.

Try white paper, but also tonal and black papers. I like to use brown parcel paper as it has a bit of texture, it’s cheap, and you can buy a roll and have the freedom to cut it to any size you want.  White charcoal or even chalk, is a great to get the highlights onto the paper and to create your full tonal range.

After you have trialed and experimented with using Charcoal on different papers, you should take on a still life drawing to test your technique.

Final Still Life

Less is more. One object or three objects…don’t go too far. Think of the scale of your piece-it can be bigger than what you did for graphite-especially if you are using blocks of charcoal.

Composition is important. If doing fruits, think of their interesting textures from inside as well as outside. Zoom in and think about placement on your final page.

Whole objects are not necessary and can focus your observation and make the piece more interesting too.


What paper will you use? This would have been decided from your previous trials with charcoal. Brown parcel paper perhaps to make the scale larger and involve white chalk too? White A3+ paper to capture some textures and work on main shadows?

Make time to set the composition and trial many variations before deciding on the final one. Do careful observations of the main forms and objects, then you can start to add the tones and details.

I will demonstrate in my next facebook live how I go about a still life using charcoal, in case you are anxious to start.

See you there 🙂


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OCAD Studio: Low Key Landscape Sketch – Part 3

  • In this final session we will be adding all the lovely, golden points of light on the opposite shores.
  • To make sure all the dark tones are saturated, you will need to begin by washing over some of your medium (all over the whole image).
  • This will ensure that the painting is as dark as it will be when varnished and it will also provide a nice smooth layer to paint the glowing lights into.
  • Next you will need to paint in some pure burnt umber where the lights will be.
  • Use your small detail brush for all of this as you will need to be precise with these tiny brush strokes.
  • This will create a value transition for the warm light colour into the cool landscape colours.
  • Then take dobs of pure cadmium yellow and paint them inside the burnt umber patches.
  • They should blur slightly as they transition into the burnt umber.
  • Once you’ve added cadmium yellow, the only thing left to do is paint pure titanium white within the cadmium yellow.
  • This will make it feel like the yellow lights are really glowing out of the dark surrounds.
  • Copy this process for all the lights in the painting and their reflections in the water.
  • Once you’ve done this you should have succesfully balanced out the gloom with some lovely points of light.
  • Small oil painting surface (primed canvas, panel or oil paper)
  • Burnt Umber, Titanium White and Cadmium Yellow oil paint
  • Small pointed brush
  • Mineral spirits and linseed oil
  • Easel
  • Palette
  • Palette cups