Jonah's Handcrafted Soap Co. makes its bars mostly by cold process, so that's the method this page covers in the most detail. Hot process and melt and pour are summarized further down. Read Lye Safety first, and run every recipe through the Lye Calculator.

Cold process (CP), step by step

Cold process gives you the most control over ingredients and designs, but the bars need weeks to cure.

What you need

• A digital scale (grams are easiest), splash goggles, chemical-resistant gloves, long sleeves

• A heat-safe plastic or heavy glass container for the lye solution (never aluminum, tin or zinc)

• A stainless steel or heat-safe plastic pot or bowl for the oils, a stick blender, silicone spatulas

• A thermometer, a mold (a silicone-lined loaf mold is common), and a cutter for bars

• Your recipe, checked in two lye calculators and printed or saved

The steps

1. Gear up and clear the space. Goggles, gloves and long sleeves on. Kids and pets out of the room, and good airflow.

2. Weigh everything separately: oils and butters, lye, and the liquid.

3. Make the lye solution. Slowly add the lye to the liquid (never the reverse), stir until it dissolves, then set it aside to cool. It can get close to 200°F. For milk or other sugary liquids, use the frozen-liquid method on Lye Water & Other Liquids.

4. Melt the hard oils and butters, then add the liquid oils. Mixing in the cooler liquid oils helps bring the temperature down.

5. Check temperatures. Soap Queen notes that soaping at 140°F or above can crack the tops, and at 100°F or below makes soda ash more likely. Around 120°F helps prevent deep soda ash. Milk soaps are kept much cooler.

6. Combine. Pour the lye solution into the oils. Pouring it over the stick blender's head cuts down on splashes and air bubbles. "Burp" the blender by tapping it on the bottom to release trapped air.

7. Blend to trace. Alternate short pulses of the stick blender with stirring until the batter thickens and drips leave a trail on the surface. Thin trace is best for swirls. Thicker trace holds texture on top.

8. Add fragrance, color and additives at the stage your recipe says, usually at thin trace. Use fragrances tested for cold process, at or below the supplier's IFRA Category 9 limit (see Additives, Fragrance & Color).

9. Pour into the mold and tap it firmly on the counter to release bubbles. Texture the top if you like.

10. Gel or no gel. Insulating the mold (covering it with a box or towel) lets the soap heat up and "gel," a darker, translucent stage. Gel brightens colors and helps prevent soda ash. Spraying the fresh top with 99% isopropyl alcohol also helps against ash. To skip gel (for milk soaps, for example), put the mold in the fridge or freezer.

11. Unmold after about 2–3 days for most recipes. Soft, high-olive recipes can take longer, and sodium lactate in the lye water helps them unmold sooner.

12. Cut into bars, then cure them (below). Keep gloves on while cleaning up, because fresh batter can still irritate skin.

Curing cold process soap

• Cold process bars need about 4–6 weeks. Saponification is mostly done within a day or two. The cure lets the extra water evaporate, so the bar ends up harder, milder and longer-lasting in the shower.

• 100% olive oil (castile) bars can take much longer. Bramble Berry notes up to 6 months to fully harden.

• Cure the bars spaced apart on a rack or open shelf so air can reach every side.

• Weigh a few bars at the start and end of the cure. Water loss changes the weight, which matters for the net weight on your label.

• Store cured bars somewhere cool, dry and dark. This also helps the scent last (Bramble Berry).

Other methods

Hot process (HP)

Hot process cooks the soap so saponification finishes before you mold it. The bars can be used sooner, though they still get better with a cure. They look rustic rather than smooth. 1. Make the batter as for cold process, usually in a slow cooker. 2. Bring it to trace, then cook on low, stirring now and then. It goes through stages until it looks glossy and like thin mashed potatoes or petroleum jelly. In Soap Queen's tutorial this took about 30 minutes. 3. Cooked soap is very hot (around 160–180°F). Keep your gear on. 4. Stir in fragrance and additives, then press the thick soap firmly into the mold. 5. Unmold when firm and cut. A few weeks of curing makes a harder, longer-lasting bar.

Melt and pour (M&P)

Melt and pour starts with a ready-made soap base. The lye step was done at the factory, so you don't handle lye. It's a good way to start, and it's great for kids' projects with an adult. 1. Cut the base into cubes and melt it gently in short bursts in the microwave or a double boiler. Don't let it go over about 140°F or boil it, because it scorches. 2. Add skin-safe fragrance (Bramble Berry suggests about 0.3 oz per pound) and colors made for M&P. 3. Pour into molds. Spritz the top with 99% rubbing alcohol to pop bubbles and help layers stick. 4. Let it harden fully, then unmold and wrap it right away in plastic wrap. M&P bases attract moisture from the air ("glycerin dew" or sweating). 5. No cure needed.

Sources - Soap Queen: Back to Basics: Lye Safety Guide. https://soapqueen.com/bath-and-body-tutorials/tips-and-tricks/back-to-basics-lye-safety-guide/ - Soap Queen: Soapy Mess-Up Quick Guide (2–3 days in mold; pouring lye over the blender; gel and soda ash; glycerin dew). https://soapqueen.com/bath-and-body-tutorials/tips-and-tricks/soapy-mess-quick-guide/ - Soap Queen: Explaining and Preventing Soda Ash. https://soapqueen.com/magicpod/explaining-preventing-soda-ash/ - Soap Queen: Luck of the Irish Hot Process Tutorial (cook on low to a Vaseline-like stage, about 30 minutes). https://soapqueen.com/bath-and-body-tutorials/cold-process-soap/luck-irish-hot-proces/ - Soap Queen: Hot Process Series: Crock Pot Camo (cooked soap around 160–180°F). https://soapqueen.com/bath-and-body-tutorials/cold-process-soap/hot-process-series-crock-pot-camo/ - Handcrafted Soap & Cosmetic Guild: Hot Process Soap for Beginners. https://www.soapguild.org/tools-and-resources/resource-center/71/hot-process-soap-beginners - Soap Queen: How to Avoid Burnt Melt & Pour (do not exceed about 140°F). https://soapqueen.com/bath-and-body-tutorials/tips-and-tricks/how-to-avoid-burnt-melt-pour/ - Bramble Berry: Beginner's Guide to Melt and Pour. https://www.brambleberry.com/beginner/beginners-guide-to-melt-and-pour.html - Soap Queen: 5 Tips for Layering Melt and Pour Soap (alcohol spritz). https://soapqueen.com/bath-and-body-tutorials/5-tips-layering-melt-pour/ - Makesy: How Long Does Bar Soap Need to Cure? (4–6 weeks; water evaporation; saponification within 24–48 hours). https://makesy.com/blogs/news/how-long-does-bar-soap-need-to-cure - Bramble Berry: Beginner's Guide to Common Soap Making Oils (castile up to 6 months to harden). https://www.brambleberry.com/beginner/beginners-guide-to-common-soapmaking-oils.html - Bramble Berry: How to Prevent Scent Fading in Soap (store cool, dry, dark). https://www.brambleberry.com/soap/scent-fading.html - Soap Queen: How to Store Handmade Bath Products. https://soapqueen.com/magicpod/store-handmade-bath-products/