Updated: Dec 2, 2020
There are many types of moulds used in resin creating. When purchasing, remember that if it has a shiny side where resin will be poured, the piece will come out shiny too. If it is matte/dull, the resin piece will also come out dull/matte. Some of the less expensive ones may deteriorate sooner, but they can also be a good way to learn and start your resin casting journey off more economically.
All moulds do wear out eventually for a variety of reasons, and some will loose their shine sooner then others as well, and become more dull over time. But there are ways to take care of a mould so it will last longer, and keep its shine longer.
Torching is a popular way to pop bubbles in resin, but it can cause the silicone to fuse to the resin piece, and when you try to separate it from the mould, it will tear and ruin your mould. Never use a large torch with small silicone moulds. Kitchen or chefs torches can be too direct and too hot, but if it can be controlled and turned down a bit that would be better. A chefs torch could be used once you know how to manipulate it so it doesn't ruin your moulds or scorch your resin. It's best to use as low a flame as possible, but don't let the flame touch your resin or mould. Barbecue lighters are more suited for the smaller moulds, as the flame isn't as strong. Try to find the type you can adjust the flame on. Keep the flame high above the piece, and never go near the mould. It's actually the co2 from the lighter (flame) that is popping the bubbles so you don't need to get the flame right up to the resin. You can use a toothpick to push bubbles away from the edge. or heat up a metal needle or pin to help pop bubbles. Heat guns are often also suggested to reduce bubbles, but they too can cause overheating, & fusion of moulds to resin so be careful with those too. Craft embossing hot air guns are also often used. Each artist tends to find their own preference after experience.
Some artists will suggest and swear by using isopropyl alcohol, in a fine spray mist, to pop bubbles instead of heat. However, just be aware many resin manufacturers do not recommend that, as alcohol might affect the cure negatively, and it can break down the Epoxy where it contacts. If you choose to spray alcohol, it is at your own risk, and be aware that it "could" produce an undesireable cure finish. Using isoprophyl alcohol seems to be becoming a popular method for popping bubbles in resin when people are not understanding how to control & use the heat method. It's not ideal, but if going to do so, you will have the best success if you use a VERY fine mister spray bottle and spray from a distance. If the alcohol droplets are too big or too close, they will leave pinholes or other marks in the resin once cured. Some users say the alcohol will pop the surface bubbles, but you may have to do it multiple times, like every 15 minutes (set a timer), for an hour depending on resin being used (and if any inclusions are sending bubbles up too). If using alcohol misting methods, the alcohol needs to be higher percentage alcohol content 91% or above (99% is better), so there is not too much water content. Especially important with Liquid Diamonds. If you've sprayed alcohol over your resin, do not use a flame right after. The alcohol has to have time to dissipate first, to reduce risk of starting a fire.
Ideally, you want to reduce potential for bubbles prior to pouring in the moulds. One key thing you can do, is ensure the resin is not cold, and has no to low bubbles prior to pouring in to the mould. Use silicone or plastic utensil to stir instead of wooden sticks (they can release air in to resin when stirring). Stir thoroughly, but not vigorously, a slow stir, scrape sides and bottom now & then. There are other tips in the Liquid Diamonds and ArtWorks information tabs on our website, and there is a separate blog post about reducing bubbles.
Try not to use your nails or harsh scrubs or scrape, to clean your moulds because it can effect the shiny surface. Just wash with gentle soap and water, then allow to air dry. Water spots can be removed with a gentle cloth or soft paper towel, but don't ever rub your moulds, or use anything that might scratch them, as that will translate over on to your next piece casted. Many people use tape to remove dried resin from moulds that is stuck in spots. Alcohol can also deteriorate moulds sooner, so do not use alcohol to clean or wipe your moulds. And if creating with alcohol inks, be prepared they reduce the life of your mould as well.
Resins can also cause added issues for mould life. Excessive heat from overheating resin can cause your mould to be become dull prematurely. If a resin is poured past it's depth threshold, or organics added that create overheating or moisture (due to not being dried thoroughly), or too much colourant added to create overheating, or resin that started it's cure in mix cup (sitting too long) prior to being poured in mould, can cause premature exotherm, and overheat in mould. If resin goes into pre-mature exotherm, it can get extremely hot, which can fuse resin to the moulds too. Pre-mature exotherm can also cause resin to pre-maturely yellow, & cause it to be fragile & crack easily.
Casting resins such as Liquid Diamonds Casting Resin, are specifically designed for use in moulds, and yield best results when used properly. Many projects require pouring in layers, so the resin does not overheat. There is lots of information available about both Liquid Diamonds and ArtWorks Resin use in casting, on their information pages on our website, plus even more in my long Blog post also on website, called "All About Working with Resin Guide for ArtWorks and Liquid Diamonds" (full of helpful tips).
Top-coating, art resins, counter and other types of non-casting resins, are not designed for use in moulds. That said, many artists do like to use them because it's what they have on hand, or quicker cure times, viscosity, etc. ArtWorks Resin cures in half (or sooner) the time of Liquid Diamonds Casting Resin, so some of our customers do use ArtWorks Resin in their moulds if they are shallow (less then 1/4" pours), or willing to pour in numerous shallow layers of less than 1/4" each time and layer. With Liquid Diamonds we suggest you let it sit in cups for 5-10 minutes, before pouring In to moulds. With ArtWorks resin, it’s not the same, & ideally we suggest it does not sit in mix cup too long before pouring into moulds, but it can sit a bit (5 minutes is fine in smaller cups) to help remove bubbles. Just keep an eye on it, make sure it doesn't sit too long that it warms & gets hot. Once the two parts of resin kit are mixed together, they do begin their cure cycle (even while sitting in the cup). ArtWorks with it's thicker viscosity, is meant to be poured on to surface areas shortly after mixing, so a premature exothermic reaction doesn't start to occur in the cup. If resin is getting warm in the cup, it has been left to sit too long (or if colour was used, the ratio may have been off). Adding too much colourant (over 8-10% ratio to resin, can also cause resins to go into premature exotherm as well.
Larger resin mixes will cure faster, and smaller mixes and shallower moulds will cure slower and take longer. Cure times will vary depending on mass and temperatures and additives. With Liquid Diamonds, a 30 gram (2-3 oz mass) is roughly about 16-24 hours based on room temperature of 77F (25 celsius), so if room is colder, it can take longer to cure. For lower amounts and lower temperatures, it will take longer to cure. Also, please note, that mould shapes can effect the process too. Spbere's for example, will hold in the heat more, and may need to be poured differently with layers then a mould that is wide open and doesn't hold the heat in.
When working with your moulds, keep the ones you use for resin, for resin only. Do not use them for any other projects. Once moulds are worn out, and shine is gone, you can repurpose them for concrete or other non resin casting type projects if desired.
Try not to stretch your moulds too far when removing objects, as it can also wear down the shiny surface or tear the mould. When trying to remove resin cast pieces from your mould, try running a bit of water and mild dish soap between mould and piece, and slowly work it down to help gently release the piece.
There are mould release agents some people like to use. Your experience may differ from anothers, so sometimes trial and error is best way to see what your own preference will be. On quality made moulds, you can use a 100% silicone oil (bicycle lubricant), on your mould to help keep it conditioned. Rub it all over, and let sit for a few days to fully absorb and recondition. It can potentially help prevent your mould from drying out faster. When you do this though, you will need to allow the mould to rest between castings, so the oil fully evaporates before next casting, so don't do this until you can give your mould a several day break from use.
Storing your moulds properly also helps keep their shape. Many people keep the original packaging moulds are shipped in, to store them as well. Some store in plastic drawers or boxes. Just be sure they're protected and not getting crushed or bent, warped or marked in storage.
Happy casting and I hope this info might help to save or prolong the life and condition of your moulds. :)
This image below: shows a mould on the left, that has worn out. The shine is gone, and the edges have relaxed and no longer hold the shape. The image on the right, shows a mould that still has it's shine (can not see in photo), and the edges are still firm and supportive.