The Complete Guide to Handmade Soap Making in the UK: Solid Soap, Liquid Soap & Castile Soap Base Explained

Handmade soap making has become increasingly popular across the UK, whether for personal use, gifting, or launching a small business. With growing awareness around ingredients and sustainability, more people are choosing to create their own soaps using high-quality raw materials.

This comprehensive guide will walk you through everything you need to know about making solid soap using caustic soda (sodium hydroxide), liquid soap using caustic potash (potassium hydroxide), and the easiest alternative—ready-made Castile liquid soap base. You’ll learn the science behind soap making, detailed recipes using grams and litres, safety guidelines, and how to choose the best method for your needs.

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What Is Soap and How Is It Made?

Soap is created through a chemical process called saponification, where fats or oils react with an alkali (lye) to produce soap and glycerin.

In simple terms:

• Oils (such as olive or coconut oil) + Alkali (NaOH or KOH) = Soap + Glycerin

There are two main types of soap you can make:

• Solid soap (bars): Made using sodium hydroxide (NaOH)

• Liquid soap: Made using potassium hydroxide (KOH)

Although both processes are similar, the type of alkali used determines whether the final product is hard or liquid.

Understanding the Key Ingredients in Soap Making

Oils and Butters

The oils you choose determine the properties of your soap. Common options include:

• Olive oil: Creates a gentle, moisturising soap

• Coconut oil: Adds hardness and strong lather

• Shea butter: Provides nourishment and creaminess

Example blend for beginners:

• 500g olive oil

• 200g coconut oil

• 100g shea butter

Alkalis Explained

Sodium Hydroxide (NaOH)

Used for making solid bar soap. It creates a hard, long-lasting product.

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Potassium Hydroxide (KOH)

Used for making liquid soap. Produces a soft paste that dissolves in water.

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Additives

You can customise your soap with:

• Essential oils (10–30ml per kg of oils)

• Natural colourants (clays, micas)

• Exfoliants (oatmeal, coffee grounds)

Making Solid Soap with Caustic Soda (NaOH)

Solid soap is the most traditional form of soap making and is ideal for beginners willing to follow safety guidelines.

What Is Caustic Soda?

Caustic soda (sodium hydroxide) is a strong alkali essential for saponification. While it is hazardous in raw form, it is completely transformed during the soap making process.

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Safety Precautions

• Always wear gloves and goggles

• Work in a well-ventilated area

• Always add lye to water (never water to lye)

• Keep away from children and pets

Step-by-Step Solid Soap Recipe

Ingredients:

• 500g olive oil

• 200g coconut oil

• 100g shea butter

• 120g sodium hydroxide

• 300ml distilled water

Instructions:

1. Prepare the lye solution
   Slowly add 120g sodium hydroxide to 300ml water. Stir carefully until dissolved. Let cool to ~40°C.

2. Heat oils
   Melt and combine oils, heating to around 40–45°C.

3. Mix together
   Slowly pour lye solution into oils while blending.

4. Blend to trace
   Use a stick blender until mixture thickens (trace stage).

5. Add extras
   Add fragrance (10–20ml) or colour.

6. Pour into moulds
   Leave for 24–48 hours.

7. Curing process
   Remove from mould and cure for 4–6 weeks in a dry space.

Making Liquid Soap with Caustic Potash (KOH)

Liquid soap requires a slightly more advanced process but offers flexibility for hand washes, body washes, and cleaning products.

👉 where to buy potassium hydroxide for liquid soap UK online:
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Why Use Potassium Hydroxide?

KOH creates a soft soap paste that dissolves in water, resulting in a liquid product.

Liquid Soap Recipe

Ingredients:

• 700g olive oil

• 300g coconut oil

• 180g potassium hydroxide

• 600ml distilled water

Instructions:

1. Prepare lye solution
   Dissolve 180g KOH in 600ml water.

2. Heat oils
   Heat oils to ~70°C.

3. Combine and blend
   Mix lye solution into oils and blend.

4. Cook the paste
   Cook mixture (slow cooker method) for 2–3 hours until it becomes a thick paste.

5. Dilution stage
   Add 1–2 litres of hot distilled water gradually until desired consistency.

6. Cool and customise
   Add fragrance or essential oils (15–30ml per litre).

The Easy Alternative – Ready-Made Castile Liquid Soap Base

If you want to skip handling lye entirely, a ready-made base is the best option.

👉 where to buy castile liquid soap base UK online:
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What Is Castile Soap?

Castile soap is a vegetable-based soap traditionally made from olive oil. A ready-made base allows you to customise without complex chemistry.

How to Use Castile Liquid Soap Base

Simple Recipe:

• 1 litre Castile soap base

• 10–20ml essential oil

• Optional colour

Instructions:

1. Pour base into container

2. Add fragrance

3. Stir gently

4. Bottle and use

Benefits

• No lye handling

• Beginner-friendly

• Time-saving

• Consistent results

Safety Guidelines When Working with Lye

• Use protective gloves and eyewear

• Always mix in ventilated areas

• Store chemicals in sealed containers

• Label everything clearly

Common Mistakes Beginners Make

• Incorrect measurements (always weigh in grams)

• Skipping curing time

• Mixing at wrong temperatures

• Using wrong alkali (NaOH vs KOH)

Solid vs Liquid Soap – Which Should You Make?

Scaling Up for Small Soap Businesses

If you plan to sell soap:

• Scale recipes proportionally (e.g., 5kg oils batches)

• Track all measurements carefully

• Use consistent suppliers

• Store products in cool, dry conditions

Why Buy Soap Making Chemicals from HD Chemicals?

• High purity ingredients

• Reliable UK supplier

• Suitable for hobbyists and businesses

• Bulk buying options available

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Conclusion

Soap making is both a science and an art. Whether you choose to make solid soap with sodium hydroxide, liquid soap with potassium hydroxide, or use a ready-made Castile base, each method offers unique benefits.

For beginners, starting with a Castile base is easiest. For those ready to explore traditional methods, working with lye opens up endless possibilities.

FAQs

1. Is caustic soda safe for soap making?
   Yes, when used correctly, it fully reacts and does not remain in finished soap.

2. Can I substitute NaOH with KOH?
   No, they produce different types of soap.

3. How long does soap need to cure?
   Typically 4–6 weeks.

4. Why is my soap soft?
   Too much water or incorrect oil ratios.

5. Can I make soap without lye?
   All real soap requires lye, but you can use ready-made bases.

6. What oils are best for beginners?
   Olive oil and coconut oil.

7. How do I calculate lye amounts?
   Use a soap calculator for precise measurements.

8. Why is my liquid soap cloudy?
   Impurities or incorrect dilution.

9. How long does liquid soap last?
   Typically 6–12 months.

10. Is Castile soap suitable for sensitive skin?
    Yes, especially when made with pure olive oil.

🧪 Sodium Hydroxide (Pearls) – Technical Specification

Product Overview

Sodium Hydroxide (NaOH), commonly known as caustic soda, is a highly alkaline inorganic compound supplied in solid pearl form. It is widely used in soap making, cleaning products, water treatment, and chemical manufacturing.

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Chemical Identification

Physical Properties

Purity & Composition