Floral casting does take some practice and experimenting, so do plan to try a few pieces first before making an important keepsake. It is important to have patience when learning this craft.
You have a few options with floral casting. There are many many resins that do different things, and people have different preferences for each task at hand. Deep pouring casting resins degas much easier in a mould, but they often take a lot longer to cure. You'll want a resin that does not tend to bubble easily for this type of craft. Not always, but often coating resins are a 1:1 ratio, sometimes not a thin viscosity, and tend to cure faster so may not be ideal for bubble release. Casting epoxy resins are often a 2:1 ratio and thinner viscosity which allows for better bubble release. We find many floral preservation artists love working with Liquid Diamonds Casting Resin for this particular type of project. No pressure pot is needed, and they can achieve stunning & clear results. For best results view and practice the instructions for keeping bubbles to a minimum prior to pouring.
You do need to ensure that when you are using organics such as florals, that they are completely dried out, and have no moisture remaining prior to casting in resin. If they are not dried out, they may turn colour or brown inside the resin and possibly eventually rot. Many floral artists like to use silica gel. Although called a gel, silica is actually the consiseancy of sand.
One product often used (& available in Canada), is called Activia Flower Drying Silica gel. Often sold at Michaels, Walmart, Staples & online. Or you can dry them out using other methods as well, but the key is they must have zero moisture left in them. Start with about a 1/2" of silica gel in the bottom of a plastic container, then gently & slowly add more until you cover them fully. Put the lid on to seal well. Follow directions for the product you're using to dry flowers. Depending on the size & thickness, and moisture of the flora, they could be dry in a week or so. Gently remove from silica gel sand, and use a soft cosmetic brush to carefully remove any residue that doesn't shake off. Silica gel left on flowers in resin castings can appear to some as bubbles.
Some people like to use the Micro-fleur drying product that dries flowers between a press in the microwave, some do not like that way.
Be mindful that florals may change colour once added to resin, and also once subject to any UV/sun even once in resin.
If you get bubbles on the sides of your mould, use a toothpick to pull them up take them out of the resin. But careful not to scratch your mould doing so.
Be careful not to bruise your flowers by handling them without gloves. Oil from your fingers can sometimes transfer to the floral petals, and you may not see them prior to setting in resin, but it may show afterwards in the resin, looking almost see through. Some people like to seal their flowers first prior to setting in resin, but many prefer not to. You do not need to do so, however some floral artists find it helps with less bubbles, and colour preservation. If you are a floral preservation artist, you likely know to use gloves when handling customers florals, however prior to receiving bouquets, you have no control over how many people may have touched the petals in a bouquet (from the people picking them at a farm, to the florists making the bouquets, to the wedding day where it's often handed off to others). Just try to instruct your customers to be careful where possible for best preservation opportunity. While bouquet is not in use, keep it in a vase to protect it, and keep it upright when possible, try not to lay the bouquet down on its side.
Some artists use a spray lacquer. Hairspray is typically not recommended. Some sealing products can burn delicate florals, but resin can if not careful as well. Some people only spray their lighter coloured florals to help with UV protection. Some people will actually paint the petals a bit first so they keep & hold a vibrant colour. There is a resin spray by Castin Craft that you can use to spray the florals first.
Keep in mind it is possible some organics possibly may cause discolouration. For people who want to specialize in floral preservation, it is best to test their own organics to see how they react. If you receive florals that you have found may cause that, it is best to find a way to seal those prior to casting. Another thing to keep in mind, is yellow or gold in castings often reflect a yellow glow in to & through the resin, so if using those colours, you may find a different appearance in the over all piece.
If trying to do a dandelion burst, spray it very lightly, not too close, with an acrylic sealer or type of sealer (although not a necessesity, many people cast them without sealing too) . Fill mould about 1/4' of the way with Liquid Diamonds, then place dandelion puff on top. Let is sit for 4 hours, then gently pour more resin around the sides until it's fully encased in resin (for a mould size between 3 to 7 cm).
When placing your flowers, there should ideally be resin underneath first. Be careful not to push dried floral petals down or they may separate and end up floating. It's best to pour a thin layer (or preferred depth for space), let it set a bit. Then add your florals, then pour a thin layer over your florals and let it dry, also to allow them to stay where you want them to, and not to be able to float up. Once that layer is set, and flowers are sturdy (depends on what you're working with), you can then decide based on your resin brand directions, how deep your following layers will be. Most people find it best, when it comes to working with florals, to work in layers. With some florals, and some resins, if it's too deep a pour, you can accidentally burn your flowers if the resin overheats from being poured to deeply in a mould at one session. This is why many floral preservation artists work in layers only. There is no set timing or depth for every flower or resin.... this takes practice to learn in your environment, with type of resin being used as well. Another reason it's safer to pour in layers to avoid added risk of ruining someones bouquet.
Also important note, if you are working in a mould that is more enclosed (such as a sphere mould), they tend to hold in more heat (as resin heats up to cure), so you will need to pour in shallower layers than you would in wide open moulds that can release the heat easier.
Ideally figure out your design, prior to setting in resin. Some people prefer to work in the mould placing florals face up so they can see the design well as they go. Some moulds require you to work with top of piece facing the bottom (like some sphere's).
If you're using glitters, they may sink to the bottom (unless they're very fine glitter), while flowers float to the top, so you must plan in advance for different additives. And if you're not sure, you may need to practice on a smaller scale with different additives as well to learn how they all work in the type of project you are planning.
When it comes to popping any bubbles, there are many schools of thought. Some prefer to use a (long neck style) barbecue lighter, and carefully hold it so flame is about an inch above the resin and mould. Never let flame touch your resin or mould, as you can accidentally fuse your mould to the resin piece, or singe your resin. Some people like to to use a light mist of 99% isoprophyl alcohol to pop their bubbles instead of a torch, but if you use too much it can effect your cure, plus weaken your mould.
Once piece is removed, there is sometimes a need to dome coat a piece or sand & polish it. It is easier to dome coat some pieces, but not necessarily depending on the item.
This blog will have a bit more information added soon. Plus I will soon add a separate blog post about sanding and polishing, and another about doming.