#anodizing #aluminum #making #caswell #metalwork # Quick Start Read [[#Safety]] first. Then work the five tanks in this order, never touching the part bare-handed after step 2: 1. **Wire the part** to a length of titanium wire (from the kit). Mechanical, tight — a poor connection is the #1 cause of failure. 2. **Degrease** — 5 min at 140 °F in SP Degreaser bath. Rinse. Water-break test (water sheets, doesn't bead). 3. **De-oxidize** — 1–3 min at 110 °F in Aluminum De-Oxidizer. Rinse. 4. **Anodize** — 60–75 °F, **4.5 A / sq ft for 90 min**, air agitation on. Acid (+) goes to the part, lead GP plates (–). Rinse. 5. **Neutralize** — quick dip in baking-soda bath. Rinse. 6. **Dye** — 15 min at 140 °F. Rinse. (Skip for clear anodize.) 7. **Seal** — 15 min at 210 °F in nickel-acetate seal. Wipe dry, hit with WD-40, cure 24–48 h. The **720 Rule** sets the math: `720 = (amps / sq ft) × minutes / mils`. Caswell's LCD spec is 4.5 A/sq ft × 90 min ≈ 0.56 mil coating — fine for color. For 1 mil, run 160 min. ==Tomorrow: confirm power supply situation before mixing acid — Standard Kit does not include a rectifier. See [[#Power Supply]].== # Overview This is the Caswell **Low Current Density (LCD)** process — type-II sulfuric-acid anodizing scaled for home use. The part is the anode in a dilute sulfuric-acid bath; passing DC current grows a porous aluminum-oxide honeycomb on the surface. Dye soaks into the pores; a hot seal hydrates the oxide and locks the dye in. Source: Caswell Plating Manual Version X (2012), pp. 105–113. The kit ships with chemicals, lead cathodes, titanium wire, mist suppressant, and an air pump — but **no power supply, no sulfuric acid, and no dyes**. Buy those separately before starting. # Resources - [Standard Anodizing Kit product page](https://caswellplating.com/standard-anodizing-kit.html) - [Caswell instructions portal](https://support.caswellplating.com/portal/en/kb/caswell-inc/downloads/instructions) - [720 Rule calculator](http://www.caswellplating.com/720.html) - [Caswell customer forum](https://forum.caswellplating.com) — search anodizing threads before posting - Caswell Plating Manual Version X (PDF, in `/uploads/manualvx.pdf`) — primary source for everything below # Equipment ## What's in the Standard Kit - SP Degreaser (2 lb) - Aluminum De-Oxidizer / De-Smut (2 × 1 qt) - Anodizing Sealant — nickel acetate powder (1 lb) - Mist Suppressant (4 oz) + Mist Control Balls - 2 × GP Plates (lead cathodes, 8" × 8") - Anodize & Chrome Stripper (1 lb) - Titanium hanging wires - Aluminum tank bar - Air pump + airline (bath agitation) - 0.1 Ω shunt resistor (for measuring current with a multimeter) - Color wheel + 5 × 6061 practice strips - Ceramic heaters (sized for Caswell's 6-gal tanks) ## What I have to add | Item | Purpose | Source | |---|---|---| | Battery acid (sulfuric, 1.26 baum), 1 gal | Anodize bath | NAPA, part # BAT-9002 | | Distilled water, ~10 gal total | All baths — never tap | Grocery store | | Anodizing dyes | Color | Caswell ([dyes page](https://caswellplating.com/anodizing-products/anodizing-dyes.html)) | | ==Power supply / rectifier== | Drives the anodize | See [[#Power Supply]] | | Half-face respirator + acid-gas cartridges | Safety | 3M 6000-series with 6003 cartridges | | Acid-resistant gloves (nitrile or butyl, not latex) | Safety | — | | Splash goggles or full face shield | Safety | — | | Baking soda, big box | Acid neutralize + spill kit | — | | Candy / aquarium thermometer | Bath temp | — | ## What I'm substituting - **2-gallon white HDPE buckets with lids** instead of Caswell's 6-gal tanks. Recipes below are scaled to 2 gal. HDPE is fine for sulfuric acid at this dilution, the deox, and the dye — but HDPE softens around 130 °F, so the **210 °F seal bath does NOT go in a plastic bucket**. Use a stainless pot on the stove or hot plate for sealing. Confirm bucket recycling code is **2 (HDPE)** or **5 (PP)**. - **Anova sous vide** for temperature control on the dye bath (140 °F — perfect) and possibly the seal (marginal — Anova tops out around 197 °F vs. the 210 °F target). See [[#Sous Vide Notes]]. ## Power Supply Caswell explicitly says battery chargers do a "barely passable" job — they're rated for charging batteries, not driving a grounded load, and have no current control. They also note that a 12V/10A charger only delivers ~10.8 V at 5 A under real load. Two options, in order of preference: 1. **Benchtop variable DC supply, 0–30 V / 0–10 A, with constant-current (CC) mode** — e.g. Riden RD6012, Korad KA3010. ~$80–150. CC mode is the right tool: set the target current and let voltage float up as the oxide insulates. Caswell endorses CC for "any and all anodizing applications." 2. **12 V battery charger + 600 W lamp dimmer on the AC input + the 0.1 Ω shunt + multimeter to read current.** Caswell explicitly endorses this fallback (manual p. 107, Figure 6). Cheaper, but you're chasing the dial. For a 2-gal bath with parts up to ~1 sq ft surface area, **5 A delivers 4.5 A/sq ft**, which is the LCD design point. Wiring: **stranded copper insulated leads** to the aluminum tank bar; the tank-bar-to-part connection must be **aluminum or titanium** only. Copper in the bath contaminates it. # Chemical Recipes (Scaled for 2-gal Buckets) Caswell's official recipes are for 4–4.5 gal tanks; everything below is scaled by ~0.45×. Always **add acid to water**, never the reverse. | Bath | Distilled water | Chemical | Temp | Time | Agitation | |---|---|---|---|---|---| | **Degrease** | 1.8 gal | 16 oz SP Degreaser | 140–200 °F | 5 min | None | | **Deox / De-smut** | 1.5 gal | ~24 oz De-Oxidizer (≈3/4 of one 1 qt bottle) | 110 °F | 1–3 min | None | | **Anodize** | 1.5 gal | 0.5 gal battery acid + 1 tsp Mist Suppressant + mist balls | 60–75 °F | 90 min @ 4.5 A/sq ft | Air pump | | **Neutralize** | 0.5 gal | 4 oz baking soda | Ambient | 30 sec dip | Hand-swirl | | **Dye** | 1.5 gal | 3 oz Caswell dye (3/4 of a 4 oz bottle; warm water to 180 °F *before* adding dye) | 140 °F | 15 min | None | | **Seal** | 1.9 gal | 2 oz Anodizing Sealant | 210 °F | 15 min (or 2–3 min per 0.10 mil) | None | Label each bucket permanently with a marker: **DEGREASE / DEOX / ACID / DYE**. Never cross-contaminate. Lid them when not in use. # Process Detailed steps from Caswell manual pp. 110–112, adjusted for my setup. ## 1. Prep - Polish, bead-blast, or scratch-brush to the finish you want — anodize is *transparent* and will show every flaw underneath. - Break any sharp edges (1/32" radius minimum). Anodize pores grow perpendicular to the surface; sharp edges get almost no coating and dye unevenly. - If the part has been anodized before, **strip it first** in the Anodize & Chrome Stripper (1 lb in 4 gal distilled water; immerse until color is gone, ~3 min). ## 2. Wire up Titanium wire from the kit, wedged or bolted into a tapped hole on the part. The wire-to-part contact **must be mechanically tight** — the joint also anodizes, and a loose joint insulates itself and kills current mid-run. Caswell calls this the #1 failure mode. After this step, **do not touch the part with bare hands** — fingerprints leave oil that won't dye. ## 3. Degrease (5 min @ 140 °F) Lower into the SP Degreaser bath. No agitation. After 5 min, pull, rinse with a distilled-water spray. **Water-break test**: water should sheet evenly off the surface. If it beads or spots, the part is still dirty — re-degrease. ## 4. De-oxidize (1–3 min @ 110 °F) Lower into the De-Oxidizer / De-Smut bath. This removes the natural oxide layer and any smut (especially important on Japanese motorcycle castings with zinc content). Rinse with distilled spray. ## 5. Anodize (90 min @ 4.5 A/sq ft, 60–75 °F) - Bath at room temp. If under 60 °F, drop in a glass heater briefly to bring it up; if over 75 °F, ice bottle on the side. - Turn on the air pump. - Place the part. Tank bar to **(+)**, GP plates to **(–)**. Switch on power. - Set the rectifier to **constant current at 4.5 A/sq ft**. Voltage will start low (a few volts) and climb to 12–16 V as the oxide grows. - Watch for **Peak Anodic Resistance (PAR)** — the amperage drops off when the film stops growing. That's the cutoff. - 90 min is the rule of thumb for ~0.5 mil coating (good for color). Use the [720 Rule](http://www.caswellplating.com/720.html) for other thicknesses. - Rinse with distilled spray. ## 6. Acid neutralize Quick dip in the baking-soda bath, then rinse with distilled water. **Don't skip this** — acid carried into the dye tank streaks, blemishes, and eventually shifts the dye's color. ## 7. Dye (15 min @ 140 °F) - Work fast. The longer the part sits after anodizing, the more the pores close up and reject dye. Dye while pores are fresh. - Lower in, no agitation. 15 min for solid color. - Rinse in distilled water. - For fade / gradient effects, hand-dip in stages — see manual pp. 114+ (Inexpensive Fade Anodizing by Bryan Pryor). ==Red dyes are picky== — pH must be 5–6, film thickness 0.5–0.7 mil, seal must be at a true boil. Other colors are forgiving; red is not. ## 8. Seal (15 min @ 210 °F) - **Use a stainless pot on the stove or hot plate**, not the HDPE bucket. Plastic warps above 130 °F. - Pre-heat the sealant bath to 210 °F. - Lower the part in. No agitation. 15 min (or 2–3 min per 0.10 mil oxide thickness). - Pull, wipe dry with a soft cloth, immediately apply a light coat of mineral oil (WD-40 fine) to even out the finish. ## 9. Cure 24–48 hours in a dry, ambient-temp area to reach final hardness. Don't handle aggressively before then. # Sous Vide Notes The Anova circulator is useful but has limits: - **Dye bath (140 °F) — ideal use.** Anova holds 140 °F rock-solid. Drop the bucket in a larger container, or run the Anova directly in the dye bucket. Stainless skirt will stain — dedicate the unit to anodizing and don't reuse for food after. - **Seal bath (210 °F) — marginal.** Anova maxes at ~92 °C / ~197 °F. That's below Caswell's 210 °F seal target. The hot-seal reaction does work at lower temps with longer times, but Caswell specifically calls out that red dye bleeds badly if the seal isn't at a true boil. **For red, or for the best finish on any color, use a stove/hot plate + stainless pot to hit a real boil.** The Anova is a fine "good enough" for non-red colors at extended time (30–45 min instead of 15). - **Degrease (140 °F) — works.** Same as dye bath, just a different bucket. - **Anodize bath (60–75 °F) — do NOT use the Anova.** Acid mist will corrode the stainless skirt and ruin the impeller. The acid bath stays at ambient or gets cooled with an ice bottle. ==Decision: dedicate the Anova to anodizing — get a second one for cooking, or be willing to deep-clean and accept staining.== # Safety Sulfuric acid, sodium hydroxide (degreaser), and acid mist are all real hazards. Caswell's safety section (manual pp. 5–6) is required reading. **PPE every session, no exceptions:** - Acid-resistant gloves (nitrile or butyl — **not latex**) - Splash goggles or full face shield - Chemical apron, long sleeves, closed shoes - Half-face respirator with **acid-gas cartridges** (3M 6000 series + 60923 or 6003 cartridges) when mixing acid or running the anodize bath **Setup:** - Work in the garage with the door open and a fan moving air **across** the bath and out the door. Not a basement. Not an enclosed room. - Keep an open box of baking soda within arm's reach for acid spills. - Eyewash bottle on the bench. - All buckets labeled with permanent marker. - Catastrophic-spill plan: place containment trays under each bucket sized to hold the bucket's full volume. **Rules:** - **Always add acid to water, never water to acid.** Acid-to-water is exothermic and may spatter. - **Never leave a plugged-in heater unattended.** Caswell flags this as a fire risk — the ceramic heaters can ignite if the bath boils dry. - **No metal vessels.** HDPE/PP buckets, stainless pot for seal only. - **No copper in the anodize bath.** Copper contamination ruins the chemistry. Tank-bar-to-part connections are aluminum or titanium only. - **No bleach near any tank.** Bleach + acid = chlorine gas. - **No closed/sealed containers in the anodize bath.** Hydrogen gas comes off the cathode and needs to vent. - **Lid every tank when not in use.** They will get knocked over. # Decisions - **Decision**: Go with the constant-current benchtop rectifier (not battery charger). - **Why**: Caswell's manual explicitly recommends CC for all anodizing; battery-charger + dimmer approach works but is fiddly and the manual itself describes the limits. - **Alternatives**: Battery charger + 600 W lamp dimmer + 0.1 Ω shunt + multimeter. Cheaper but more babysitting. - **Decision**: Use stove/hot plate + stainless pot for the seal bath instead of trying to push the Anova past its limit. - **Why**: Caswell says seal must be at 210 °F (a true boil); Anova maxes at 197 °F. Red dye specifically requires a true boil to seal properly. Better to do it right once than chase mystery bleed-out. - **Alternatives**: Anova at 197 °F with 30–45 min extended seal time. Acceptable for non-red colors. - **Decision**: 2-gal HDPE buckets for everything except seal. - **Why**: HDPE handles dilute sulfuric, deox, dye, and degrease fine. Service temp ~130 °F limits the 140 °F dye bath but is fine for the brief immersion window. Sealing at 210 °F is out. - **Alternatives**: Buy Caswell's 6-gal tanks (\$). Skip for now — 2 gal handles parts up to ~1 sq ft surface area, which covers everything I'm likely to do early. # Troubleshooting | Symptom | Cause | Fix | |---|---|---| | Part won't dye / dye washes out | Sealed in tap water, weak seal, dyed too late after anodize, oxide too thin | Use distilled water; seal at 210 °F for full time; dye immediately after rinse; run anodize longer | | Burn marks / pitting on part | Voltage ramped too fast, bath too warm, current density too high | Use CC mode; keep bath 60–75 °F; stay at 4.5 A/sq ft | | Streaks / blotches in dye | Acid carried into dye tank | Always neutralize + rinse before dye | | Fingerprints / un-dyed spots | Touched the part after degrease | Wire up *before* degreasing; never touch with bare skin | | Current drops mid-run | Wire-to-part connection insulated by its own oxide growth | Re-wire with tighter mechanical contact; use titanium wire | | Red dye bleeds / fades | Seal not at true boil, wrong pH, film too thin | Stove + stainless pot to hit real 210 °F; check seal pH 5.5–6.0 | | Brown/black where colors overlap | Dying across the color wheel (e.g. blue + orange) | Check color wheel — overlap adjacent colors only | | Sharp edges undyed | Anodize pores can't grow on a sharp edge | Break edges to 1/32" radius before anodizing | # Stripping Existing Anodize When you need to remove a prior anodize layer — re-doing a part, fixing a bad result, or prepping a previously-anodized stock piece — there are two paths: the Caswell stripper that came in the kit, or a DIY lye (NaOH) bath using drain cleaner from the hardware store. The DIY path is cheaper and uses chemicals you can buy anywhere. ## TL;DR for the DIY Lye Strip - **Buy**: pure sodium hydroxide (NaOH), 99%+, in bead/crystal/flake form. Common product names: **Roebic Heavy Duty Crystal Drain Opener** (Home Depot, Lowes), **Instant Power Crystal Lye Drain Opener** (Walmart, Amazon), or **MaxTite Caustic Soda Beads 99%** (Amazon). All three are essentially the same chemical. - **Avoid**: anything labeled "Drano Max Gel" (contains bleach — chlorine gas risk), "Drano Crystals" (contains aluminum chips — defeats the purpose), Rooto / "Liquid Lightning" (those are *sulfuric*, wrong chemical), or any drain product that lists surfactants/bleach/fragrance on the label. **Read the label — you want only "sodium hydroxide" as the active ingredient.** - **Dilute**: **¼ cup NaOH per 1 gallon distilled water ≈ 5% solution.** Always add the lye to the water, never the reverse — it's exothermic and the wrong order can flash-boil and spatter caustic solution. - **Container**: HDPE/PP bucket (your white anodize buckets are fine) or stainless steel. **Never aluminum, zinc, or tin** — lye eats those metals just like it eats the anodize. - **Strip**: dip the part. It will fizz aggressively (hydrogen gas — that's normal). At room temp, full strip takes **30 min – 2 hours** depending on coating thickness and seal quality. Warming to 120 °F speeds it to **5–20 minutes**. - **Watch it.** NaOH strips the oxide *and* keeps attacking the base aluminum after the anodize is gone. Pull every few minutes to check. Industrial spec is "never more than 1 minute at 10% / 110 °F"; the hobby 5% room-temp version is more forgiving but the principle is the same — over-soak and you'll lose dimension and surface detail. - **Rinse thoroughly** in tap water then a distilled rinse. ## Concentration Reference | Concentration | NaOH per gallon water | Use case | |---|---|---| | 2% (mild) | ~75 g / ⅓ cup | Slow strip, more control, room temp | | 5% (typical hobby) | ~190 g / ¼ cup (slightly heaping) | Standard strip, 30 min – 2 hr room temp, 10–20 min at 120 °F | | 10% (industrial) | ~380 g / ½ cup | Fast strip (30–60 sec at 110 °F), aggressive — easy to over-etch | Weights are for solid NaOH beads/crystals. If you buy a *liquid* drain cleaner (e.g., concentrated 27–50% NaOH solution), dilute proportionally — adjust by the ratio of label concentration. ## Surface Aftermath NaOH leaves a **satin/matte etched finish** — it does not preserve a polished surface. The lye attacks the underlying aluminum and roughens it slightly. This is fine if you're re-anodizing (you can re-polish or bead-blast afterward), but if you want to preserve a specific finish under the anodize, use the Caswell stripper (less aggressive on the base metal) or strip mechanically. The Caswell Anodize & Chrome Stripper in the kit is a milder formulation that's gentler on the base aluminum — preferred when finish matters. Recipe: 1 lb stripper in 4 gal distilled water, immerse until anodize is gone (~3 min for typical Type II coating). ## Safety NaOH is **more dangerous than the anodize bath acids** for skin contact — it causes deep, slow-onset chemical burns that often don't hurt at first but penetrate deeper than acid burns. Treat it with at least as much respect as the sulfuric. - **Splash goggles, full face shield ideal, nitrile gloves (not latex), apron, long sleeves, closed shoes.** - **Ventilation** — hydrogen gas evolves vigorously as aluminum dissolves. Garage door open with a fan, same as for the anodize bath. No open flames. - **Always add lye to water, never reverse.** This is the #1 lye safety rule. The reaction is exothermic; reverse order can flash-boil and throw caustic solution. - **Vinegar** (white, household) is the mild neutralizer for skin/surface splashes — **not baking soda**. Baking soda neutralizes acids; lye is a base, so you want a mild acid. Keep a quart of vinegar within arm's reach for the strip bath, in addition to the baking soda you keep for the acid baths. - **No aluminum vessels.** Lye will eat through a thin aluminum container fast enough to cause a spill. HDPE/PP or stainless only. - **Lid and label the bath** with permanent marker: **LYE / NaOH / STRIP**. Caustic solutions look like water. - **Disposal**: at full strength, the spent strip bath is hazardous waste (high pH + dissolved aluminum). Small hobby quantities can usually be neutralized to ~pH 7 with vinegar or muriatic acid (slowly, with stirring, monitoring with pH strips) and disposed per local rules. Don't pour caustic-as-is down the drain. ## Quick Test If you're not sure whether a piece is anodized, drop a tiny bit of 5% NaOH on an inconspicuous spot. Anodized aluminum will fizz immediately as hydrogen evolves. Bare aluminum will also fizz, but more slowly and with a different "feel." Bead-blasted bare aluminum and unanodized 6061 react fast enough that this test is more useful on polished or unknown stock. ## When NOT to Use NaOH - **Titanium anodize.** NaOH does not effectively strip titanium oxide at room temp — see [[Titanium Anodizing#Stripping Ti Anodize]] for the right approach. - **Mixed-metal parts.** If the part has steel inserts, brass fittings, or any other metal embedded, lye will damage the aluminum around them at different rates and may leave you with a problem worse than the one you started with. Mask or disassemble first. - **Cast aluminum with deep porosity.** The lye gets into the pores and keeps reacting after rinse. Use a milder bath or the Caswell stripper. # TODO - ==Buy power supply (benchtop CC rectifier ~$100–150)== - ==Pick up battery acid at NAPA (BAT-9002, 1 gal)== - ==Order dye sample pack from Caswell (6-color, ~$106)== - ==Confirm buckets are HDPE (recycling code 2)== - ==Acid-gas respirator cartridges + spare nitrile gloves== - ==Set up garage workspace: catchment trays, fan, baking soda within reach== - ==Run first practice on a 6061 aluminum strip from the kit — track amps, voltage, time before doing anything real== - ==Decide: dedicate one Anova to anodizing, or accept it'll be ruined for food== # Build Log ## 2026-05-26 - Bought the [[Caswell Standard Anodizing Kit]] - Created this note from the official Caswell Plating Manual Version X (2012) - Recipes scaled from 4–4.5 gal to 2 gal buckets - Identified gaps in kit: no rectifier, no acid, no dyes - Plan to start tomorrow after the power supply and acid are sourced # References - Caswell Plating Manual Version X, pp. 105–113 (LCD Anodizing) and pp. 5–6 (Safety) — `/uploads/manualvx.pdf` - [720 Rule calculator](http://www.caswellplating.com/720.html) - [Caswell instructions portal](https://support.caswellplating.com/portal/en/kb/caswell-inc/downloads/instructions) - [Caswell forum — anodizing section](https://forum.caswellplating.com)