DIY Soap Cutter – A Simple Guide for Cutting Your Soap into Bars

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How to Make a Soap Cutter - DIY Soap Cutting Guide for Homemade Soap

If you’re looking for a way to consistently cut your homemade soap loaves into bars so that they the same size every time, then you need a soap cutter! There’s no need to purchase expensive equipment to do this, especially if you’re just starting out. Instead, craft your own handmade diy soap cutter.

How to Make a Soap Cutter - DIY Soap Cutting Guide for Homemade Soap

The measurements for this soap cutter are made to pair up with my tutorial on how to make wooden loaf soap molds. It can be used for both melt and pour glycerin soap and homemade cold process soaps. To get started you’ll need either craft wood or plywood that is 3/4″ thick, some screws, wood glue, an electric screwdriver and a saw in order to make your cuts. If you aren’t able to cut your own wood, you may be able to find a friend, neighbor or parent to give you a hand. (My dad made mine for me.) I have also heard that if you purchase wood from Lowe’s that they will cut to your specifications.

How to Make a Handmade Soap Cutter DIY

The two sides of your soap cutter should be cut to measure 6 1/2″ long by 5″ high. The bottom piece to your soap cutter will need to measure 6 3/4″ long by 3 1/2″ wide. The front stop – which keeps your soap from sliding out to ensure bars are all cut the same size – should measure 5″ long by 2″ high.

Assemble your soap cutter so that the bottom fits in between the two sides. The sides should rest flat on the surface with the bottom in between. Apply wood glue to hold the sides together and clamp until dry. Then put several screw into the side for extra hold. Now glue the front stop to the front of the soap cutter and screw in. Finally, use a saw to cut guides down the two sides and slightly into the bottom piece of wood. These cuts determine the size of your bars. About 3/4″ in make standard size bars in width. Make the cuts further out – 1″ or more – for thicker bars. Make sure the cuts are wide enough that the tool of your choice you’ll be using for cutting will fit into these slits. I use a Chef’s knife to cut my soaps with this soap cutting guide.

Making homemade cold process soap for the first time? Be sure to check out my DIY Soapmaking Tutorial as well as my Beginner Cold Process Soap Recipe.

How to Make A Wooden Cold Process Loaf Soap Mold

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How to Make a Wooden Loaf Soap Mold for Cold Process Soap Plus Where to Buy Lye

I’ve had some people ask me how to make a basic wooden loaf soap mold for cold process soap, so I thought I’d share a tutorial on how to make your own soap molds. This wooden cold process loaf soap mold is so easy to make and it will last forever. My dad is handy with wood and power tools so he made me a bunch of these, however, if you don’t own power tools, it’s possible to get the pieces for the molds cut at no charge.

DIY Wood Soap Mold for Cold Process Soap - How to Make Your Own Loaf Soap MoldsEach of these homemade cold process soap molds will hold approximately 2.75 lbs. of (cured) soap and will make approximately 10-12 4oz. bars depending on how large you cut them. If you’re having trouble figuring out how much your soap will weigh once cured, my average recipe for one of these molds uses 36oz.  in oils & butters (fats) prior to adding the lye/water, and fragrance.

How to Make a Wooden Soap Mold - Measurements and Instructions - Works for Cold Process and Melt & Pour Soap when Lined - Plus Where to Buy LyeTo create one mold you’ll need to use wood that is 1/2″ thick. I used craft wood from Lowe’s. I have been told that if you are buying wood that an associate at Lowe’s will cut it down into the dimensions you use if you ask. For the two long sides, you’ll need to cut two pieces of wood that measure 12″ x 4″. The two short sides should be cut to 3 1/2″ x 4″ and the bottom piece of the mold should be cut to 3 1/2″ x 11″. The final dimensions of the soap mold will measure (from the outside) 12″ Long x 4 1/2″ Wide x 4″ High.

You’ll need to use wood clamps and wood glue to assemble your mold as pictured above. The two short sides fit on the inside of the two longer sides to form a rectangle and the bottom piece of the mold fits on the inside bottom of the mold. Use glue and clamps to hold the pieces together until dry. If you don’t have clamps or want to add extra reinforcement, you can use a cordless screwdriver to place screws where the sides connect.

Making a lid for these is optional. Honestly I’ve never needed to use a fancy lid as cutting cardboard to fit on top of the molds works just fine during the curing process. I simply place cardboard on the top of the filled mold and then cover with towels to insulate during the 24 hour saponification period.

How to Line a Wooden Soap Mold for Cold Process SoapLining your soap molds before use is essential to being able to get your soap out of the mold. If you don’t line your mold, your soap will get stuck. I used to cut parchment paper to line my molds as demonstrated in this the same process that this tutorial by Inner Earth blog uses with contact paper. Basically you fold the paper in a way that is similar to wrapping a present but with an open top. However, parchment paper and contact paper can be expensive and the process for lining molds this way can be tedious and time consuming especially if you are making multiple or large batches at once. Because of this, and due to the stiffness and occasional pain in my hands from the fibro, I use trash bags to line my molds. If you’re practical and don’t mind a few minor creases on the sides and bottom of your soap, then this method may be the one for you.

I got this ideas from another local soapmaker who I used to sell alongside at our local Farmer’s Market. She used large 20 gallon kitchen trash bags to line her molds, then once she unmolded the soaps, she’d re-use the trash bags for actual trash. (Plus the soap gave them a nice, fresh scent.) What I use are thin, clear office trash bags. I bought a huge box of 1000 10 gallon light duty commercial trash bags to line my molds with as they a lot less expensive than parchment paper and can be used again for my office trash. (They are super cheap at Sam’s Club and office supply stores.) To line a mold I simply unfold the bag – but don’t open it – press it into the mold and then tape the outer edges where the bag folds over the outside of the mold to keep it in place. This method is gentle on hands and super quick. I can now line all nine of my molds in 5 minutes or less. Of course, how you choose to line your molds is personal preference. I recommend doing whatever works best for you.

Once your soap has set you simply lift the soap from the mold and peel off the liner, cut into bars and allow to cure a minimum of 3-4 weeks.

To use these molds for melt and pour glycerin soap, simply line with trash bags as indicated for cold process soap.

Looking for lye?

On a side note, I wanted to share with you where to buy sodium hydroxide (lye) for making your soap. You used to be able to buy Roebic brand lye from Lowe’s. 2lb. ran $8.99. Several months ago I noticed that their price for a 2lb. container of Roebic lye had gone up to $16. Recently, they stopped carrying it all together. I imagine this has something to do with the illegal meth labs that seem to be sprouting up everywhere. Therefore what I recommend is to look in your local yellow pages for a local chemical supply company. I am lucky enough to have one in my hometown called ChemSolv. ChemSolv sells 99% pure sodium hydroxide (which is suitable for soapmaking) in 55lb. bags. These bags with tax – in case you don’t have a resale license – runs $38 and change. They currently have locations in Roanoke, VA (my hometown), Colonial Heights, VA, Piney Flats, TN and Rock Hill, SC. I purchase what they call caustic soda beads.

If you don’t have a chemical supply store near you, you can buy 2lb. containers of Food Grade Sodium Hydroxide from Amazon. Even with shipping, these containers run cheaper than 2lb. containers of Roebic brand lye from Lowe’s – assuming your store still carries it. Plus, currently if buy 5 2lb. containers of lye, you receive $5 off your purchase. You can also find Potassium Hydroxide Flakes for liquid soapmaking available through the same company through Amazon with the same deal. Other brands of lye you can use include Red Hot Devil Lye Caustic Soda Beads and RED CROWN High Test Lye.

If you are just venturing into making homemade soap and want to learn how to make soap, be sure to visit my DIY Cold Process Soapmaking Tutorial. Or if you’re looking for skin conditioning bar of handmade soap, check out my Skin Loving Natural Cold Process Soap Recipe. (It will fit into one of the wooden soap molds described above but will make large square bars – about 5 1/2oz. – 6oz. each – rather than rectangular bars of soap.)

DIY Soapmaking – How to Make Cold Process Soap

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Go here for a revised, updated and expanded tutorial on how to make cold process soap from scratch.

DIY Cold Process Soapmaking

Handmade Honeysuckle Soap from Rebecca's Soap Delicatessen

Soapmaking can be a lot of fun and very rewarding. However, it’s not something to just jump right into without first some research and understanding of the process. Not only are there precautions that need to be taken when making cold process soaps, but a failed batch can be a very expensive lesson.

Because of the many dangers associated with soapmaking due to the use of lye – also known as sodium hydroxide – and the plethora of information to be had, I recommend that you carefully research the process before starting out on your own. Details on where to obtain additional information will be included within this article.

Soapmaking involves a chemical process in which sodium hydroxide (lye) reacts with oils to make soap. This process is called saponification. Because this process requires the use of lye, important safety precautions must be taken. Rubber gloves and safety glasses should be worn during the soapmaking process, and vinegar, which neutralizes the lye, should be kept on hand in case of an accidental spill for clean up. However, water and not vinegar should be used to flush lye from skin if contact occurs. In addition to the necessary safety equipment needed for your journey into making cold process soap, there is other required equipment you’ll need to get started.

First and foremost you will need to acquire lye. Because without lye, there is no soap. The main components to make a true bar of soap are fat(s) – such as oils and butters – and an alkali – more commonly known as lye. You should be able to find lye in the plumbing section of your hardware store, at a local chemical supply store, or online. For those just getting started and without the need for a 50lb. bag of lye available from chemical supply stores, you can buy Roebic Heavy Duty Crystal Drain Opener in 2lb. containers at Lowe’s stores. (It contains 100% sodium hydroxide also known as caustic soda.) Alternatively, Red Devil Lye can be purchased online. The brand doesn’t really matter, but it must be 99% or more pure sodium hydroxide. (If you are local to Roanoke, VA you can purchase 50lb. bags of sodium hydroxide beads locally in 50lb. bags from ChemSolv. Just be sure to transfer your bag of lye to a plastic container or double garbage bag lined box that you can seal after opening.)

In addition to the lye, you’ll also need a large pot for mixing the soap. I recommend a large stainless steel pot. What type of pot you use is up to you, however, your pot cannot be aluminum. Lye reacts badly with aluminum so remember to never mix the two. You’ll also need an accurate scale to weigh your ingredients in either ounces or grams. You can use digital postal scale from an office supply store. Just be sure the scale is calibrated properly and can handle the amount of weight you will be using. You’ll also need a thermometer or two to measure the temps of your oils and lye solution. And, you’ll find that a stick blender– also known as an immersion blender – is your best friend in making soap. You can hand stir, but this method can take you hours over minutes and a stick blender also ensures even distribution of ingredients. And then of course there are the molds, soapmaking oils, and distilled water to be mixed with the lye.

There are several types of molds you can use to create cold process soap. You can purchase tray molds that are basically hard plastic molds that will create numerous bars of soap at once. These molds should be marked suitable for cold process soapmaking since the soap gets very hot during the saponification process. You can also easily build a mold from wood, with a bottom and four sides. This type of mold will produce a log of soap that you would then cut into slices. When using a wooden mold, you must line it with parchment paper to aid in easy removal of the soap. (Freezer paper is not a good idea as it melts to the soap and mold.) Lining your mold is sort of like wrapping a present except that you are wrapping the inside of the box rather than the outside. It takes some practice to get it right. The parchment should then be secured with tape to the mold. Alternatively, you can line your mold with plastic film or a plastic office sized garbage bag. Just be sure to tape the material to the top of the mold for easy removal. You can learn how to make your own wooden soap molds here. (You can also make silicone soap molds.)

Next, we’re on to oils. The soapmaking oils are an important part of your soap. The types of oils you use will determine the properties that your soap will have. For example, three of the most popular soapmaking oils, especially for beginners, are olive oil, coconut oil, and palm oil. The olive oil helps create a moisturizing bar with a stable lather; coconut oil produces a hard, cleansing bar with a fluffy lather; and palm oil makes for a hard bar with a stable lather. Each of these oils has its own SAP (or saponification) value which determines how much lye should be used in the soap recipe for saponification to occur in such a way that it makes soap. Too much lye and you have an unusable bar of soap. Not enough and you could end up with a really soft soap with excess oil. A great source for learning more about the saponification process and the properties of various soapmaking fats & oils is Susan Miller Cavitch’s book The Soapmaker’s Companion. Her book also contains a great troubleshooting section and several of her own recipes. When creating your own recipes for soap, there are also a lot of additional free resources to help you with this process. Lye calculators, for example, will automatically calculate the amount of lye you need in a recipe based on the amounts and types of oils you plan to incorporate into your recipe. You can find multiple links to lye calculators by conducting a google search. Although I like to use the lye calculator at Majestic Mountain Sage. It is good practice to always double check the amount of lye in a recipe with a lye calculator if you are unsure of its source.

Let’s get down to business!

So, I guess by now you’re wondering just what you do with all of that lye and oil and equipment. Well, I’ll tell you. You make soap! Your best bet is to start by preparing your mold so that it is ready when your soap is ready to be poured. You’ll also need to cut out cardboard that will fit over the top of your mold. The cardboard will be used to help insulate your soap after it is made. Once these steps are complete, you would then measure out your distilled water as called for in the recipe you are using.

Measuring distilled water for soapmaking

Measure the amount of distilled water called for in your recipe out in fluid ounces.

Pour your distilled water into containers

Pour your distilled water into a non aluminum container. (I like to use plastic pitchers.) Weigh your lye for your soap recipe

Next, measure out your lye. Be sure you have on all of your safety gear for this. Lye gets VERY hot, and chemical burns are never any fun. Be sure to have vinegar open and close by for any spills. For the lye, you will be weighing the amount needed with your scale. Place the container you’re using to measure the lye onto the scale, press tare to zero it out, then slowly pour the lye onto the scale until you reach the amount needed.

Pour the lye into the distilled water

Then slowly pour your lye into the water, never the other way around as it could result in a not so pleasant volcano effect. Stir your lye into the water with a plastic or wooden spoon until it dissolves. Now set it aside to cool. If you’re mixing the lye inside, keep it on the stove with the exhaust fan turned on and step away. Or allow it to cool outside to avoid the nasty fumes. Be sure there are no children or animals underfoot who could get hurt.

Weigh out your soapmaking oils

Next we’re on to the oils! While the lye is cooling, you can weigh and melt your oils. I normally melt my oils all together in a large pot on the stove at medium heat. You can also melt the oils separately in canning jars within a water bath. First, however, you must weigh your oils on the scale. Weigh each oil individually. Set your container on the scale, hit tare so it zeros the weight, then slowly add the oils to the container until you’ve reached the weight the recipe calls for.

Soapmaking oils melting in stainless steel pot on stove

Repeat this process for all oils and fats in your recipe. I usually start with the solids first so I am adding the liquids to the pot last. Stir the oils until they are completely melted, then remove from heat.

Adding lye-water to soapmaking oils

Once your lye has cooled to at least 120 degrees F, though I find I like to use my lye-water solution between 95 and 100 degrees F, you can generally begin pouring the lye-water into your oils. The temperature of the oils can vary depending on what the recipe you are using calls for, but the oils should not be hotter than the lye. If you aren’t sure how a recipe will react at higher temps, then mix at between 95-100 degrees F. (Refer to The Soapmaker’s Companion for information on why temperatures matter.) With your handy stick blender ready to go, very slowly pour the lye-water into the oils.

Mixing soap

Begin stirring with the stick blender on low. As the lye and oil begins to incorporate, you can switch the blender to high. Stir well, moving the blender all over the bottom of the pot and up through the soap mixture.

What soap looks like at trace

You will continue to stir until you reach what is known as trace. When the soap has reached trace, it will sort of look like cream of wheat or a custard. When you pull the blender through the soap, it should leave a line following it, and if you pull some of the soap up then drop it on the surface of the soap, the soap should be able to support that drop. Should you not reach trace, within 15 minutes, you can rest for about 15 minutes, then start mixing again. Some oils used in soapmaking are slower to trace. Olive oil, for example, can take a much longer time to trace than other oils unless it is mixed with other oils whose properties promote a quick trace.

You would stir in any additives you’d like to use in your soap, such as fragrance or collodial oatmeal, once your soap has reached a light trace where it is just barely leaving a trail or supporting a drop. Mix these in well, especially any essential or fragrance oils, so you won’t have any “hot spots” in your soap. Generally fragrance oils account for 3-6% of your soap, but be sure to follow manufacturer’s recommendations if they are available. Note that some fragrances and essential oils can accelerate trace. Once your additives have been thoroughly incorporated, you’re ready to pour your soap into its mold!

Pouring soap into the mold

Slowly pour your soap into the prepared mold. Drop the mold with the soap onto the counter several times to help remove any air bubbles.

Cover and insulate your soap molds

Next, cover the mold with cardboard. You may tape the cardboard down onto the molds if you like. Follow this step by placing several towels or a blanket over your covered mold. This helps to insulate your soap so that the saponification process can properly occur. Your soap should then remained covered for 24 hours.

Cutting loaf of soap into bars

Once your soap has been in the mold for 24 hours, you can then remove the soap from the mold and cut into bars. I generally discount the amount of water used so that my soap can immediately be cut into bars. If once you unmold your soap, however, and find that it is really soft, then you can wait another day or two before unmolding and/or cutting your soap into bars. Once the soap has been removed from the mold, you will then need to allow your soap to cure in order to completely finish the saponification process. This generally takes a period of 2- 3 weeks. If you’re setting your soap to dry on a flat surface, be sure to set it on top of parchment or freezer paper to keep the oils from seeping out of the soap into the surface of your drying space. You can also dry your soaps on a rack. Once the soap has cured you can then package it to share with your friends and family!

If you’d like to see photos of the entire cold process soapmaking method, I’ve added an album to my fan page on facebook. You can view it here.

Still have questions?

Not everyone has a successful soapmaking experience the first go around. So if you’re still cautious after all of your research, then I recommend finding a friend who makes soap to teach you the process.

Ready, set, go!

Looking for an easy recipe to get you started? Well, here ya go.

Basic Cold Process Soap Recipe

7.2 oz. coconut oil
16.2 oz olive oil
10.8 oz palm oil
1.8 oz. shea butter

12 fl oz. distilled water
4.9 oz lye

At trace:
2 oz. fragrance oil of choice or 1 oz. essential oil of choice

Follow your basic soapmaking instructions (above) for a great basic bar of soap with a creamy thick lather! This recipe will fit into one of my wooden loaf soap molds. (Instructions on how to make a loaf soap mold here.)

Remember, if you are ever substituting an oil for another oil in a recipe, you must recalculate the recipe to get the correct amount of lye needed since different oils & fats have different SAP values. Never make a substitution without completing this crucial step.

Recommended Suppliers:

Mountain Rose Herbs
Bulk organic herbs, undiluted therapeutic quality essential oils, and bulk ingredients for soapmaking. They also carry a nice line of bottles, jars, and containers for packaging.

Natural Soap Making Kit
A natural soapmaking kit for beginners with all the ingredients you need to make your first batch of cold process soap including the lye. The box it comes in doubles as a mold.

Wholesale Supplies Plus
Large supplier of wholesale soapmaking supplies and cosmetic materials. Free shipping on everything with a low $30 minimum order.

Nature’s Garden
Wholesale candle and soap supplies with large selection of affordable, quality fragrance oils. Buy any 5 1lb. fragrance oils and get $1 off per container.

Soapmaking Resources & References:

Lye Calculator I
Lye calculator from Bramble Berry.

Lye Calculator II
Lye Calculator from Majestic Mountain Sage.

Lye Calculator III
Pine Meadows lye calculator.

Lye Calculator IV
An advanced soap calculator from Soap Calc designed to help you create the perfect soap recipe by giving you the chemical makeup and properties your ingredients will have in the finished product.

Weight Conversion & Percentage Calculator
Hate math? Now you can easily figure out what percentage of ingredients your recipe contains and easily create changes and re-formulate to suit you! Great for calculating lotions, fragrance and essential oils, etc. And now you can convert units of weight and temperatures too!

Properties of Soapmaking Oils
This chart is for looking up various fats and oils to see what characteristics they give your soap.

Non-Comodogenic Chart
This chart may help when formulating blends that are to be used on the face.

FDA Cosmetics Handbook
Regulations, Guidance, and Resources.

Herbal Infusion
Herbal Infusion Techniques for using infusions in soapmaking.

How to Re-size a Batch of Cold Process Soap
Learn how to re-size any cold process soap recipe to suit your needs by making it either larger or smaller.

Soap Troubleshooting Chart
Cold Process Soaps Troubleshooting Chart.

How to Line a Wooden Soap Mold
This series of pictures will illustrate how we make the liner used to line the wooden soap mold, and how we make the cardboard form used to shape the liner paper.

Soapmaking colours/colors from herbs and spices
Herbs and spices for coloring CP (Cold Process) and HP (Hot Process) soap.

How to Make a Wood Loaf Soap Mold
Learn how to make a loaf wooden soap mold that yields 10-12 bars as well as where to source lye and how to line a wooden soap mold.

How to Make A Loaf Soap Cutter
Tutorial for making a loaf soap cutter to cut your soap loaves into evenly sized bars.

Ingredients recognized as safe by the FDA
Substances generally recognized as safe for use.

Soap Crafting
A modern book on how to make cold process homemade soaps, this book by renowned Soap Queen, Anne-Marie Faiola, contains easy to understand information, step-by-step photographs of thirty-one soap recipes and the process as well as tutorials on advanced soapmaking techniques such as swirling, funnel pours and embedding.

The Soapmaker’s Guide to Marketing Soap Online
This ebook by established author, Lisa Maliga, offers insight into the world of a homemade soap business for beginners. It includes questions to ask to see if you’re ready to sell your homemade soaps, how to set up a shop, pricing and labeling guidelines, avoiding scams, getting found, where to buy supplies and more.

DIY Ideas for Soap Labels
Learn how to create your own non-conventional soap labels and get some inspiration for making your own.

How to Make Soap with Circle Embeds
Learn how to make decorative cold process soaps with circles embedded within each bar.

Cold Process Goat Milk Soapmaking Tips
Learn how to make homemade goats milk soap the easy way without having to worry about prepping your goat milk in the freezer first to get it to that slushy ice stage or worrying about it curdling with my simple tutorial!

How to Hand Stamp Soaps
Learn how to decorate your homemade cold process soap bars with either hand carved or store bought stamps.

Cold Process Soap Recipes
A collection of handmade cold process soap recipes with instructions and photographs of the finished soaps.

Article and photos © Rebecca’s Soap Delicatessen