The Core Set: The Cornerstone of the Type System Architecture

In type engineering, designers rely not just on a single pivotal character but on a small, critical group of characters called the "Core Set" (or Master Set). This group carries the DNA of the typeface and determines all its proportions and rules.

1. What is the Core Set?

The Core Set is a collection of 5 to 10 characters carefully selected to encompass all types of strokes, curves, and proportions required to build the remaining characters. The goal is not merely to facilitate drawing but to ensure Visual Harmony and replication of the design pattern across all characters in the alphabet.

Functions of the Key Glyphs:

• Defining Structural Rules: Through these glyphs, all fundamental metrics of the font are established: Weight and Thickness, Vertical Metrics (such as X-Height and Baseline), and Key Nodes (to ensure recurring symmetry).
• Creating Aesthetic Consistency: To ensure all characters adhere to the same style, whether sharp, rounded, or geometric.
• Saving Time and Effort (Efficiency): Once the Core Set is finalized, the designer can use techniques like duplication, rotation, and transformations to quickly build hundreds of other glyphs while maintaining accuracy.

2. Methods for Identifying and Using the Core Set

The selection of Key Glyphs varies depending on the writing system, as each glyph must represent a different type of geometric form within that system.

The Advanced Design Process:

1. Sketching: Drawing the Core Set manually or in Adobe Illustrator.
2. Quantification: Transferring the set to font software (like Glyphs) and defining precise metrics (advance width, X-Height, angle).
3. Systematic Application: Using these glyphs as templates to design the rest of the characters (e.g., using the shape of 'D' for 'Th' or 'B' for 'T' and 'Th' in Arabic).
4. Optical Correction: After the font is complete, visual weights are balanced to ensure that rounded letters do not appear thinner than straight ones.

3. The Challenge in Arabic Variable Fonts

In the context of Variable Fonts, the importance of the Core Set is amplified:

• Master Points Alignment: The control points (Nodes) in the Core Set must match between all masters (Light and Bold) so that the technology can seamlessly Interpolate or generate intermediate weights.
• Structural Complexity: Due to the contextual nature of Arabic (Contextual Forms), the Core Set must include glyphs in their different positions (initial, medial, final) to define how the character's shape transforms as the weights change.

The axial shape, or more accurately the Core Set, is the compass guiding the type designer. It is not merely a collection of templates but the blueprint that maintains the soul and harmony of the typeface, contributing critically to its legibility and technical success.