Creating Soap Colour
Once melted you need to work fairly fast, as a skin will start to form quite quickly on the surface of the soap. It is whilst fully melted that soap colour, fragrance and any other additions such as irridescent powder or dried flower petals etc. are added.
Simple food colours can easily be used, as can liquid soap colours and other water-soluble liquid colour bases. Obviously the depth of a particular colour is dependent upon how much is used. Don't be tempted to over-colour your soaps, especially if using clear soap bases, as the transparency of the finished soap will be affected if too much colour is used, plus, coloured lather in use is off-putting. Fragrance can be added either using essential oils or simple fragrance oils, which are available in a huge range of tempting fragrances these days. Again, strength of fragrance is dependent upon the amount added. For a meaningful fragrance, around 20ml fragrance per Kilo of soap (2%) is sufficient, so a few drops per single bar is fine. As a guide, a maximum of 3% fragrance addition is generally advised. Irridescent powders or glitters may float or sink to the bottom of a mould depending on their make-up, so a suspending base may be helpful if you want to avoid this. Also, glitters and sheens can become lost if too much is added, so be sparing for best results.
You will need to stir in all these additions fairly quickly and pour into whatever mould you are using before a skin forms as this will spoil the finish of the final bar. There is nothing to stop you from quickly re-heating the mixture whilst it is still in its microwaveable container, but remember that a few seconds is all it will need. Too much heat will evaporate the fragrance, so avoid this if you can.
Try not to intoduce bubbles into the soap mixture as this will also spoil the final appearance. The mixture starts to set quite quickly, trapping any bubbles or other imperfections, which is especially problematic when using a clear base to make a transparent soap. If you are able to obtain any form of denatured alcohol (rubbing alcohol is available from some chemists) you will find that 'spritzing' the surface of the soap with alcohol immediately after pouring will disperse surface bubbles and give a better finish. To obtain TSDA (trade-specific-denatured-alcohol) which is the correct product, you will require a license from HMRC. This license is free but requires correctly applying for.
If making larger numbers of bars or maybe a loaf, it is much more suitable to use the direct - heat method. That is to say, heat the required volume of soap in a suitable pan on a hob. There is no need to go to the trouble of using a double-boiler, but you must ensure you don't overheat the soap, otherwise there is a risk that it could burn, although you'd probably have to have a lapse of memory and leave it for some time for this to happen. Use a thick-bottomed suacepan over a low-medium heat
Cut the soap into small pieces to help it melt quickly and evenly. Gently heat over a low-medium setting until the mixture is completely liquid. At this stage and whilst still over a low heat, add the colour and fragrance desired. It is at this stage that irridescent powders can be added also, together with other additions for texture, such as oatmeal or desiccated coconut, which are 2 examples of useful and easily availble additions to give an exfoliating texture if desired.
The addition of extra ingredients is more leisurely using this method, as continuous low heat is available to keep the mixture from forming a skin. Again, be careful not to introduce bubbles if at all possible. Fragrance should be the last addition, as heat will cause some evaporation. Again, work on around 20ml of fragrance or essential oil per Kilo for a meaningful fragrance.
Once all ingredients are added, pour carefully and slowly into the mould and allow to cool. Larger quantities of soap will require longer time to cool. The filled mould can easily be refrigerated to speed this up. Support large moulds in a bed of sand or rice to prevent distortion. Do not store your soap in a fridge or cold conditions once it's set. Soap should be stored at normal room temperature and humidity to minimise any 'sweating', which can spoil the surface of your soap.