Oil painting Study Guide

📖 Core Concepts Oil painting – pigments mixed with a drying oil; the oil hardens by oxidation (reaction with air), not by evaporation. Supports – surfaces the paint is applied to: canvas, wood panel, or copper plate. Fat‑over‑lean – each successive paint layer must contain more oil (fat) than the one below to keep the film flexible and prevent cracks. Glazing vs. alla prima – Glazing = thin, transparent layers over a dry underpainting; Alla prima = wet‑on‑wet, finish in one session. Drying vs. curing – Drying = surface becomes touch‑dry (days‑weeks, oxidation). Curing = full polymerization (months‑year) before varnish. 📌 Must Remember Oil binders: linseed (fast drying, yellows), safflower/walnut/poppyseed (slower, less yellowing). Siccatives = drying accelerators; turpentine/mineral spirits = thinners and cleaners (reduce oil → “lean”). Support preparation: size (animal glue) → isolate support → apply gesso (traditional: glue + chalk; modern acrylic). Fat‑over‑lean rule: Lean (more solvent/less oil) → first layers; Fat (more oil) → later layers. Varnish (e.g., dammar gum in turpentine) only after painting is fully cured (up to 1 yr). 🔄 Key Processes Prepare canvas Stretch on stretcher → size with rabbit‑skin glue → apply gesso → let dry. Mix paint Tube pigment + drying oil → add siccative or medium (cold wax, resin) for desired consistency. Apply layers (fat‑over‑lean) Start with lean, solvent‑thinned paint (underpainting). Add progressively richer, oil‑laden layers; finish with thickest “fat” layer. Glazing Paint thin, transparent glaze over a dry underpainting; repeat for depth. Alla prima Block in colors, blend wet, finish without waiting for layers to dry. Curing & varnishing Allow full oxidation (months). Apply removable varnish; later can be cleaned/re‑varnished. 🔍 Key Comparisons Linseed vs. safflower oil – Linseed: fast drying, yellows over time. Safflower: slower drying, stays clearer (good for whites/light colors). Glazing vs. alla prima – Glazing: builds depth, requires dry layers, more time. Alla prima: quicker, spontaneous, less layering. Traditional gesso vs. acrylic gesso – Traditional: glue + chalk, absorbs oil, can cause brittleness. Acrylic: titanium dioxide + acrylic binder, flexible, faster drying. Canvas vs. wood panel – Canvas: lightweight, flexible, needs sizing & gesso. Panel: rigid, less movement, traditionally gessoed, good for fine detail. ⚠️ Common Misunderstandings “Oil paint dries like water paint.” – It oxidizes, not evaporates; drying can take weeks, curing months. “More solvent = faster drying.” – Solvent makes paint leaner, which drys faster but can compromise adhesion if over‑used. “Varnish can be applied as soon as paint is touch‑dry.” – Early varnish traps solvents, leading to cracking; wait until fully cured. “All drying oils behave the same.” – Different oils have distinct drying rates and yellowing tendencies. 🧠 Mental Models / Intuition “Oil → Oxygen → Hardens” – Picture paint as a sponge soaking up air; the more oxygen it contacts, the harder it becomes. “Layer cake” – Each layer is a cake slice; the bottom must be firmer (lean) so the top (fat) can stay flexible without collapsing. “Transparent window vs. opaque wall” – Glazes act like colored windows letting light through; alla prima is an opaque wall painted all at once. 🚩 Exceptions & Edge Cases Fast‑drying pigments (e.g., cadmium reds) may reach touch‑dry in a day, but the underlying film still cures slowly. Cold wax medium creates a matte, thick body that can impede oxidation; allow extra curing time. Metal supports (copper) do not need sizing; however, they can react with acidic pigments—use barrier grounds. 📍 When to Use Which Choose linseed oil for general purpose, quick work, or dark pigments. Choose safflower/walnut/poppyseed oil for light or delicate colors where yellowing is undesirable. Use glazing when you need luminous depth (portrait skin tones, atmospheric effects). Use alla prima for rapid studies, plein‑air scenes, or when you want a spontaneous, painterly look. Select traditional gesso for historic technique replication; acrylic gesso for speed, flexibility, and modern safety. 👀 Patterns to Recognize Yellowing over time → indicates linseed oil or lead‑based pigments. Cracking along a layer boundary → likely a fat‑over‑lean violation (lean layer beneath a fat layer). Glossy spots after varnish → uneven curing; thicker paint areas cure slower. Dust or “crazing” on the surface → insufficient drying before varnish or environmental humidity changes. 🗂️ Exam Traps “Oil paint dries by evaporation.” – Wrong; it oxidizes. “All varnishes are permanent.” – Many (e.g., dammar) are removable; permanent varnish is a specific synthetic type. “More siccative always speeds drying.” – Excess can cause brittleness and discoloration. “Canvas never needs sizing.” – Without sizing, acidic pigments can degrade the canvas fibers. “Acrylic gesso is the same as traditional gesso.” – Different composition; acrylic is flexible, traditional is more absorbent and can affect oil film adhesion.