Modeling form is based upon an understanding of an object's relationship to a light source. Every form is spherical and has a specific relationship to a light source(s).
Consequently, as the light rays from the light source have further to travel before meeting the surface of a form the less light is received by those areas on a form. This is due to the fact that light rays are composed of photons, which posses more light energy the closer they are to the light source. The areas on a form that are most facing the light source will reflect many light rays because many light rays can reach those areas that are facing the light source. As the parts of a form recede from the angle of the light source, they become darker in value due to the fact that they are receiving less light to reflect diffusely. It is this diffusely reflected light, created by the interaction of light on form, that enters the eye to make an image of the objects that one sees.
The illustration above shows in a constricted sense, if only 7 photons were projecting from the light source, more light rays would strike plane A than plane B, because plane A is more facing the angle of the light source. Since plane B is facing more away from the angle of the light source it receives less photons, and therefore less light, to reflect diffusely which causes plane B to appear darker in value.
More Information About Light On Form
The terminator exists at the apex of where light rays from the light source do not reach. Therefore the terminator defines the area of object that is in shadow.
On the sphere the eye does not perceive the halftone to exist in the middle of a gradation as it often is drawn in most how to draw books. In fact under a spot light scenario the eye perceives halftone to start very close to the terminator. Usually under a spot light scenario the halftone begins at 18 degrees away from the terminator, but situations can vary so much that one would have to determine how close the halftone is to the terminator just by observing it. To my knowledge, the half tone in a spot light scenario actually occurs at 30 degrees from the terminator but I am not sure why it is usually perceived at 18 degrees before the terminator. Nevertheless, this knowledge that the eye perceives halftone to exist very close to the terminator allows for a more accurate representation of the forms one is modelling.
With an understanding of diffuse reflection, the fact that half tone exists very close to the terminator and an acuteness to each forms relationship to the light source one can begin to model form.
But before the actual modelling of form begins upon a block-in, I made a poster study of the values to be used while modelling. To explain the modelling process I will use the cast drawing that I am currently working on as an example.
¹ An HB pencil was used to make this value and this value set the standard of the value range to be used in the drawing. The next values that were decided upon were the darkest value of the wall shadow, the average value of the cast shadow on the cast, the value of the highest form light and the value of the highlight(which is the white of the paper).¹ The values after the value of the shadow of a black object were decided upon by their relationship to one another (not by copying perceived values on the cast).¹ A line was erased from the value of the highest form light to decide if the value was dark enough for the erased line to read as a highlight.¹
One should know that due to the fact that the highlight has a major difference in tone in relation to the highest form light, choosing to make the highlight as evident as it appears in life causes the value of the highest form light to be quite dark and therefore causes the entire drawing to darken in compression.¹ This produces a darker drawing that will accurately show the distinction between the highlight and the form light but since the drawing as a whole will be darker the drawing will not appear to represent a white object under a spotlight. This darkening can be avoided by setting the value of the highest form light to the white of the paper and sacrificing the clarity of the highlight next to the highest form light.¹ I chose to preserve the distinction of the highlight next to the highest form light in this drawing.
One may wonder why an HB pencil would be the softest pencil to be used in a drawing of a white cast that does not encompass the entire value range. The reason is because cast drawing is also practice for painting. And with paint, one's value range is still limited because of working on a vertical plane and if one wanted to paint a subject that had more than one local color they would need skill at modelling form within a limited value range in order to not exhaust one's entire value range on an object of one local color and thus not leaving enough of the range left for objects of darker or lighter local colors.¹
Using the poster study as a guide for the value of the average cast shadow I began to fill in the shadow areas of the drawing with that value. It is necessary to flatten the entire shadow area with this value because when one is modelling form it is helpful to have a common value that one is modelling all of the forms out of. If I was to draw all of the difference in the shadow at first I would have a more difficult time understanding what the value of the darkest form light is supposed to be. Not to mention the fact that if I finished the shadow first without referring to the values that are in the light part of the form I would more than likely exaggerate the value of the reflected light.
Flattening proceeds by filling in small squares (about 1/8th of an inch wide) first with a slightly dulled pencil.¹ One is to initially fill in squares from one side to the other to the value desired.¹ This is not a type of drawing that is to be worked up in veils and is to be very direct even when modelling areas of a form that are not in shadow.¹ The evenness of this first application is a result of the right amount of pressure combined with the right amount of speed up and down while moving to the other side.¹ After the initial application there usually are many tiny dots that need to be filled in if the square is to read as completely flat. To fill it in one is to use a slightly sharper pencil and to pull out darker dots one is to use a blunted dirty kneaded eraser so as not to remove too much graphite that would create more dots to fill in.¹ The slightly sharper pencil is not to poke into the lighter dots as it is to do more the job of gently pushing the graphite from the tip of the pencil into the lighter dots to fill them in.¹ It is useful to view these squares at an angle to notice obvious dots.¹ It is also useful to throw one's eyes out of focus to notice obvious dots.¹ The squares of value are placed next to each other to stay connected.¹ Practice and experimentation with different hardness of lead and different speeds of application is the only way to improve at this. For this, I used an H pencil.
The pencil is to be sharpened then slightly dulled by rubbing it on the paper as seen in the image above because one does not want to damage the paper.¹ I am working on Artistico Fabriano Extra White, 140 lb. Hot Press paper and too much pressure can really damage this paper. This was something that I had to be very careful of while making the block-in for this drawing. It is very useful to have a really sharp pencil before dulling it down a bit. I use an Eagle 17 lead pointer to sharpen my pencil and it creates a very sharp point. Eagle 17 lead pointers can be purchased on ebay.
While flattening the shadows and even while modelling the lights the pencil is to be held at about a 45 degree angle from the paper as seen in the image above.¹ A visual example of this application of graphite can be seen in this video of students working at GCA here.
One can go right over any lines that define important information in the shadows without any fear of losing the block-in because the lines show though. Below is my flattened drawing near the before modelling form.I really only had to flatten around the area that I would be modelling first so I didn't flatten all of the shadows. After this stage I lightened the outlines from the block-in that were around the area that I was going to model so I get a better idea of what the form actually looks like.¹
Now I should explain the three step modelling process that I am practicing on this cast drawing.
¹ Gradations in this method are not decided upon by questioning if something is lighter or darker but questioning whether forms are faced more or less towards the light. And if a form needs to turn away that means it needs to get darker, if a form needs to turn more towards the light that means it needs to get lighter. The mindset for this drawing method is just as if one is sculpting the form on their drawing to accurately mimic the sculptural form(s) on a cast. Please note that all the modelling is to be done in small strips that describe the cross contour of a form.¹ In the gradation stage the strip is to laid in with strokes that run at a perpendicular angle to the direction of the largest amount of change in light on a form.¹ For example, in my diagram the sphere is lit from above, so the greatest amount of change in light on form is from top to bottom. Therefore, I laid strip number 1 with strokes that ran from left to right. It is much easier to address the holes that occur in the gradation stage when one will be marbling through them instead of against them.¹
Step 2 is Planarization or the grouping of planes. In this step one is to break the gradation into three to four distinct planes.¹ I now must say that in this drawing method each dot of graphite is not to be referred to as a value alone. Instead, in this drawing method each dot of graphite represents a micro-plane that has a specific relationship to the light. So when one is planarizing the goal of cleaning up the planes is to group each micro-plane into its respective larger plane instead of thinking of filling in or taking out dark or light spots in a value. At the completion of this stage the strip is to look like a planar version of the form. In my diagram I did not include the terminator value and reflected light in this step but usually those are added during this step.
Step 3 is Marbling. The transition from the planarization stage to the marble stage is focused on softening the harsh planar breaks, only as needed, in order to more specifically address the subtle changes in the form that one sees.¹ In this step one gains a tactile sense of the form by imagining the point of their pencil on a specific place of their drawing, looking to the same specific place on the cast and running one's eye(that is on the cast) at the same pace and direction that the pencil is moving on the drawing across a form(s) while one shifts their gaze from the cast to the drawing in order to determine whether some of the micro-planes in one's drawing need to turn more or less away from the light.¹ It is usually best to start at a definite point such as the terminator or the high form light because the only variable is for form to turn towards or away from the light from those definite points.
If this practice is specifically adhered to then one can gain the sensation of being on the form while they are marbling. The more that one marbles the more polished the form becomes. Or rather, the more specific the micro-planes adhere to their relationship to the light source. One is to begin marbling a strip by marbling along a path that describes the gradation of form with the most change. Once the major change of a strip has been accurately addressed one can marble the strip in every direction in order to address each micro-plane.¹ After this, one is to address each and every micro-planes relationship to the light source within that strip.¹ Once the overall form of the strip is accurately represented, one can and should include all detail including all the bumps and dents seen on the cast.¹
After a strip has been completed a new strip is added next to it that goes through the three step modelling process and is restitched into the previous strip during the marbling stage.¹ Please note, that for all of the strips besides the first strip one should start by including the terminator value before running a gradation. One should continue to marble the combined strips of each form as the drawing progresses. While it is good to keep strips of form next to each other for each form, with every new form one should begin with a strip that describes the most amount of change in the light on that form in order to better perceive the value range for that form.¹ It is very useful to compare back to the planes from the first form while adding new forms, in order to develop an overall relationship hierarchy in one's drawing.
There is not a specific way of looking at one's drawing during this process. One should squint, throw their eyes out of focus, use a black mirror (a piece of mirror glass that is painted black on the back so as to darken the reflection that one sees. This is about the same as squinting but much clearer.) and use conceptual ideas about form in relation to light.¹ All of these ways of seeing are tools that one should use to check one's drawing. If any inconsistencies are found in your drawing while checking it with those tools then the drawing is not accurate. One should use these viewing tools with an understanding that the value range in the drawing will be much more compressed than what one sees in life so therefore any value observations are to be determined by relationship of one to another.¹ This is very important when drawing shadows because since they are so dark I usually resort more to my black mirror than marbling while drawing them. But one can think of the form in shadows related to a light source by determining the specific light source for reflected light. Using a black piece of tinfoil to block out that are to see when the reflected light vanishes is very helpful.¹
¹ Or one could flatten the shadow value in relation to the terminator value and put the reflected light in last if one is afraid of making the reflected light too light at first. Please note, that after the terminator value has been put in the strip has to be re marbled and the dark form light has to re turn into the terminator which makes it darker.¹ This is fine because the average shadow value is just general and it is fine if the darkest form light ends up being darker than the average shadow value.
The only other thing to consider is the difference in the quality of edges. This is done mainly by relating all of the edges to the hardest edge.
Below is my cast drawing in progress from last Friday. I was still marbling the lights and flattening the shadow. I have been using an H pencil for the gradation stage and a 3H to marble. So far the darkest pencil that I have used in the shadow has been an HB. The hardness of pencil to use is determined by deciding which lead will produce the values that I desire without the use of so much force that I would scratch the paper.¹
It is very useful to surround the area that one is modelling with a dark value in order to better see subtle gradations. This is because the eye splits up gradations into 1,000 sections based upon the range of values that it sees.¹ By compressing the range of values that the eye sees by surrounding a drawing with a dark border one can better see the subtle gradations in what they are drawing.¹ It is very useful to wear a hat with a brim while modelling to get rid of the reflected light that the planes facing the light on the texture of the paper are receiving so that one can better see the subtle gradations in what they are drawing.¹
Below are some tactile evaluation analogies that have been helpful to me while I was in the marble stage of this drawing.
Rain on Tiles- Imagining the rays of light as rain that is falling onto a form. When tiles on a roof are faced most towards the rain it makes a really loud noise and when the tiles are facing less parallel to the rain a gentler sound is heard.
The Ant- The ant is pretty much the same as the marble but by imagining the point of the pencil as an ant crawling on the form that is seen one can imagine how much energy the ant has to exert while crawling on a form. This helps to make subtle rolls easier to see.
The Skateboard- The skateboard analogy was conceived by Tony Ranalli. The skateboard is pretty much the same as the ant but is imagining skateboarding across a form while modelling instead of an ant crawling.²
Any analogies that one can relate to are helpful to refer to while modelling form. And another useful tactile evaluation tool is to touch the forms on the cast that one is modelling. Touching the cast can be of great use to more accurately interpret the gradations that one sees on the cast.
¹ Jeremy Deck, personal communication, 2012.
² Anthony Ranalli, personal communication, 2012.