Resin guide – Lamella Creations

Posted on August 23, 2020August 23, 2020 by Jenny — 2 Comments

Resin mixing and curing

There are many different things that can affect resins ability to cure properly and understanding how and why this happens can help you have more successful casts. This post will cover a range of these things so that you can avoid common pitfalls and troubleshoot where any failed casts went wrong. This guide is mostly aimed at mixing and curing clear resins, but many of the points will also be helpful for other types too.

Mixing the resin

One of the most common reasons for resin to not cure properly is under-mixing. Many of the instructions sheets that come with resin just say to mix the resin for x amount of time and leave it at that. While that might be sufficient in some cases, there’s usually more factors to consider to get a properly cured cast.

The first thing to consider is what you’re using to mix with. The surface area of your mixing tool is very important as mixing with something small will give very different results from mixing with something with a nice large flat surface, as a larger surface moves the resin around more. My favourite thing to mix with is a mini baking spatula, but it will depend on the amount of resin you’re working with as to what will be best for you. The main thing to avoid mixing with is anything porous (e.g. popsicle sticks) if bubbles are a concern, as air can leech from it into the resin. Anything plastic or silicone based with a large flat surface will work well.

Once you have your tools ready, the next thing is to make sure you get the right ratio of resin to hardener. Different resins use different methods for achieving this- for epoxy or urethane resins this can either be by weight or by volume and it’s important to know which method is used for your particular resin, as otherwise the ratio will be off. If you’re mixing by weight the scales need to be sensitive enough for the amount of resin you’re mixing (e.g. bathroom scales wouldn’t be good for mixing small amounts). The more sensitive the scale the closer you can get to the correct ratio. However, it also needs to go high enough for the amount of resin you want to mix as scales have a maximum weight cut off. Many scales will state what both of these are on them so that you can choose the right one for your project.

Photo of the back and front of a small scale, showing the sticker that says 200g/0.01 — This is my smaller scale. It only weighs up to 200g but is more accurate as it goes down to 0.01g increments

The other thing that could put the ratio off is if you mix less than the minimum pour amount for your resin. With resin being fairly pricey it can be tempting to mix a tiny amount if you don’t need much for your current project, but if it’s less than the minimum it’s much more likely that the ratio will be too far off to achieve a proper cure. For example, let’s say we were trying to pour 10g total of a resin that’s mixed 1:1, but accidentally under poured the hardener by 1g. This would put the hardener amount off by 20%. However, if we were pouring 20g of resin we would only be off by 10%. The less that’s poured, the more exact the measurements have to be. Each resin is different as to how much it can tolerate being off the ratio, but for very small amounts it may not be possible to get it close enough. The other factor is that there may not be enough heat in very small amounts for the resin to cure even if the ratios were exact. Some companies will specify a minimum mix amount, but not always. In general, if you’re only mixing a few tablespoons worth it’s likely to cause problems. The minimum I try to stick to is 12g, but that’s with a heat mat for curing so it may be different for your setup.

Once you have the ratios worked out and have poured the resin and hardener, the next thing to do is begin mixing. You’ll notice that the resin will start to go cloudy and streaky- this is a good way to tell how mixed it is. When the resin’s fully mixed it should look completely clear again- if there’s any streaks it indicates that there’s unmixed hardener still. While you’re mixing it’s a good idea to scrape the sides and bottom of the cup to dislodge any hardener that gets stuck on the surfaces. Once the resin looks totally clear it’s important to then ‘double mix’ it by getting a new, clean cup, pouring the resin into it, and mixing again for a short time. This will leave behind any hardener still stuck on the sides, as scraping won’t usually get all of it. As you pour aim to transfer just the bulk of the resin and don’t wait for the rest to drip out as it’s more likely to not be fully mixed. I also like to wipe off my stirring implement before mixing again so that I know there’s no hardener sticking to that either.

Photo of a cup of resin post-mixing, showing it clear and without streaks — Your resin should look clear and not streaky again once you’ve finished mixing (this one is after vacuuming so you may have more bubbles though)

Cure inhibition

Resin mixing can be a big factor as to how well it cures but there are other pitfalls to watch out for too. One of the great things about clear resin is using different inclusions and colourants to make interesting pieces, but not everything will play nicely with resin. Water is one of the most common problems as it’s found in so many art supplies and can greatly affect how well resin cures. You can sometimes get away with a tiny amount of water if you’re careful, for example some people use a small amount of acrylic paint to colour epoxy. In general though, it’s best to avoid water based products where possible. Another commonly used colourant is alcohol inks as they can give great translucent colours, but these should be used sparingly as isopropyl alcohol will also inhibit resin’s ability to cure (but to a lesser extent than water will). Some better colourants to use include mica or other powders for an opaque look or quality resin dyes for translucent (avoid those big packs of ‘resin dyes’ you can get for cheap as they often inhibit the cure worse than alcohol ink).

Photo of 4 small bottles of resin dye with several translucent coloured resin cubes — My resin dyes with coloured epoxy blocks. The two largest ones were made with resin dyes and the smaller ones with alcohol inks. If you’re in NZ or Aussie I definitely recommend Barnes’ resin dyes

Another thing that can inhibit resin is certain silicone moulds. There are two main types of silicone used for moulds- tin/condensation cure and platinum/addition cure. Tin cure silicones are less easily inhibited themselves when making the mould, but more likely to cause resin to not cure right, while platinum silicones are easily inhibited by sulfur, but won’t cause any issues with resin curing. There are many reports of tin cure silicone causing resin to not cure on the parts touching the mould, leaving a sticky outer layer. A couple of common problematic ones are Alumilite amazing mold rubber and Oomoo series silicones. It’s common for people to buy these ones as they’re slightly cheaper than platinum cure options, but its worth the extra cost to ensure a good cast.

The last thing that can inhibit resin from curing is the age of the resin itself. Resin has a shelf life, so only lasts so long before it starts to degrade in quality. You can usually tell when this is happening as the hardener starts to yellow significantly. Using old resin can still work and the yellowing can be disguised with colourants, but there’s no guarantee that it’ll cure quite right. If you’ve controlled for other factors and are still having trouble, you may have better luck with a fresh batch instead.

Curing Environment

The last major thing that can affect resin curing is the environment in which it cures. The main factors that can affect it at this point are the humidity and ambient temperature. If the humidity is too high it can cause either the whole cast to go cloudy or just the surface exposed to air (called amine blush). Working in a climate controlled environment can help mitigate this, or even just checking the weather and not casting on days where the humidity is high. For people working with pressure pots it can also be helpful to install a moisture trap as part of your setup.

For the temperature, it’s important not to leave resin to cure anywhere that’s too cold. Resin hardens via exothermic reaction and if it’s left somewhere cold it won’t be able to generate enough heat to cure properly. Most resins will have a suggested ambient temperature that it’s best to cure at, or if you want to ensure a good cure an external heat source can help it along. Heat boxes are a common solution, they can be made from a heat lamp or warm lightbulb in a box lined with something reflective, or I like to use a cheap pet or seedling heat mat in a sealed plastic box (it also keeps the fumes in that way). Some more serious people will even use an oven set on low to help them reach full cure faster (this has to be a dedicated craft oven though and can never be used for food again). Basically any source of low heat in a container will work so you can be creative, I’ve seen one person using a reptile incubation machine to achieve this. It’s important to only use a low heat as too much can cause a runaway exothermic reaction, which can be dangerous and will ruin the piece.

Photo of a clear plastic box with a heat mat and some silicone moulds inside — My resin cure box, it has a heat mat at the bottom covered with some baking paper to catch any resin drips. The heat mat cord comes out of a hole I dremelled near the top with clay packed around it to keep the fumes in still

This guide covers a lot of points, but resin can be pretty forgiving so it’s worth just giving it a go and trying out these tips over time. You can definitely get a reasonable cast from cheap moulds and without investing in things like heat mats in the beginning. If you have any other suggestions that I’ve missed feel free to leave a comment down below.

Final useful tips

-If you’ve controlled for humidity but are still getting what looks like amine blush on your pieces, it can also be caused by some colourants or under-mixing of very finicky resins (even with double mixing)
-If you’re having curing issues that you can’t pinpoint make sure you’re not mixing with anything that could leech chemicals into the resin. I’ve seen some people mention that something in the popsicle sticks they used prevented their resin from curing, or also the wax coating from paper cups
-Make sure not to mix too much resin at once or leave it for too long if you’re using a medium to fast curing resin. When the resin is in your cup it can often be above the recommended pour depth and in some cases cause your cup to melt
-You should never have to significantly adjust the amount of hardener from the recommended amount. If you’re having curing issues troubleshoot what could be causing them, adding more hardener will just make it harder to figure out the issue and get good casts
-It can be easier to mix your resin if you first heat the resin bottle it in a warm water bath prior to starting. This lowers the viscosity, making it easier to mix the two parts together (but will also reduce the pot time)
-If you have a pressure pot/vacuum chamber, or are using a very slow setting resin you can also use something mechanical to mix your resin easier. Small paddles connected to a drill are a common option. It’s more likely to add air this way though which is why it’s only recommended in those circumstances

Posted on August 14, 2020 by Jenny — 2 Comments

Bubbles in resin

Bubbles are the nemesis of all resin crafters- while they can sometimes be used for interesting artistic effects, in most cases they’re just an annoyance that prevents you from making what you intended to. This post will cover both how to avoid bubbles in the first place and how to go about removing the ones that sneak in anyway.

Avoiding bubbles while mixing

Most resins will have a small amount of air mixed in already, but you can avoid adding more bubbles with a few simple steps. To start, when pouring the resin from its storage container into your mixing cup, avoid just pouring it into the middle of the cup- otherwise once you have a layer of resin it can start to pull air down into the resin and make bubbles. Instead, try to pour your resin down the side of the cup and you should find it fills up without adding bubbles to the mix. The same can be done with the hardener, but it will depend on your resin as to whether it’s needed (thinner hardeners are less likely to be problematic).

photo of a stream of resin being poured into the middle of a cup creating lots of small bubbles — Pouring into the middle of the cup can introduce a lot of bubbles

Next, when mixing your resin it’s important to choose a non-porous implement to mix with. Popsicle sticks are commonly recommended because they’re cheap, easy to get, and have a good surface area, but this comes at a cost. Air can leech from the wood and into your resin resulting in micro-bubbles throughout it. Anything non-porous will do, but I prefer to mix with a mini baking spatula as they’re generally made from either silicone or plastic and have a good surface area to help ensure your resin gets mixed properly. For smaller amounts of resin or to mix in colours I also use a cheap plastic paintbrush handle, the round shape seems to help somewhat in avoiding bubbles.

photo of a weighing scale, the end of a paintbrush, a small baking spatula and a vinyl glove — My mixing things look a bit gross as I’ve been using them for many years now, but they still work great. I just leave them in my cure box to let any residue set after using them

So we’ve got our resin in the cup and we’ve got our stirring implements, the next thing to keep an eye on is how you’re mixing. If you mix too fast it can whip air into the resin- mixing slow and steady takes patience, but it’s worth it for the end results (just keep an eye on your pot time!). I also find that mixing resin in too large of a cup can cause problems. Choose your cup size based on how much resin you’ll be mixing and aim to not just have a thin layer on the bottom, otherwise it gets super bubbly even with slow mixing. I like to have a range of cup sizes from shot glass up to large drinking cup so that I can choose the right one for the project at hand.

photo of 5 plastic cups in a row from small to large — I started with just a couple of sizes but it’s nice to have a range to choose from

Removing bubbles from resin

So you’ve done all you can to avoid adding bubbles but they’re still being a nuisance (or maybe you’re a perfectionist like me)? Luckily there are several different things we can do to either remove bubbles or make it so they’re no longer visible. We’ll start with the cheaper and safer options before discussing what professional resin casters use. You can also combine some of these methods together to get better results.

Option 1- Using a lower viscosity and/or slower setting resin

Resins have a large variety of properties, but the two that are important when considering bubbles are the viscosity of the resin and the cure time. These two things will dictate how well bubbles are able to rise out of the resin before it cures and they’re trapped inside. A high viscosity resin is a resin that is very thick (i.e. more like the consistency of honey than water). These resins can be useful for things like suspending glitter as it won’t sink so fast, but they have the downside of also trapping bubbles much more than a low viscosity resin will. If you don’t need the positive traits of these resins for your project it can be a good idea to instead use a low viscosity resin to reduce the amount of bubbles that will be trapped.

Viscosity will affect how difficult it is for bubbles to rise to the surface, but the other important factor to consider is how much time bubbles will have to rise to the surface. Resins that are both slow setting and low viscosity are ideal for lowering the amount of bubbles in the final cast. They will often be referred to as having ‘self-degassing’ properties as they are able to remove air without the use of other equipment. Other keywords to look out for to find resins with these properties are ‘casting resin’, ‘slow set resin’ or ‘deep pour resin’. To make sure you’ve found the right thing, check that the cure time is somewhere around 48-72 hours. If available, the TDS should also show you what the viscosity of the resin is.

screenshot from a TDS showing 1000-2000 cPs viscosity, next to a screenshot of a viscosity comparison chart showing it's approximately equal to the viscosity of glycerin — Screenshot from a technical data sheet (TDS) and viscosity comparison chart. Comparing them gives you an idea of how viscous the resin will be

Another option is to lower the viscosity of whatever resin you already have using heat, but this will speed up the cure time so you may have to work quicker than usual. The standard way to do this is to place your closed resin bottle into warm water for a bit before starting. Some people like to place the bottle into a plastic bag first to keep the water off it, but otherwise as long as you don’t submerge the lid you can just dry the bottle off before starting (make sure to do this as you don’t want water accidentally getting into your resin when you pour it). Personally I like to put my resin bottle into a yogurt maker with warm water. It’s vacuum sealed on the sides to keep the warmth in and just so happens to be the right size and shape for my bottle. Any container will do though, but it’s best to use something that won’t ever be used for food again in case there’s any resin residue on the outside of your bottle.

photo of a resin bottle in a yogurt maker — Just by chance my yogurt maker fits my resin bottle perfectly. If you’re in NZ you can usually grab a yogurt maker for $5 from any op shop

Option 2- Using a heat gun or torch for surface bubbles

One of the problems with bubbles in resin is that you can often get them to rise to the top but then they just sit on the surface and don’t pop. A good way to force them to pop is to use a heat gun, lighter, or a propane/butane torch run lightly above the surface. Using a torch or lighter is superior to a heat gun as the CO2 from the flame causes the bubbles to pop. This works great for large pours such as river tables or coating artwork where the use of a pressure pot or vacuum chamber may not be feasible. You do have to be careful not to use this on any flammable resins (e.g. polyester) or if you’ve added anything flammable to your resin (e.g. alcohol ink). Also, for any mould based work I strongly advise against using these. It’s super common to see people complaining of ruined moulds from their resin sticking to it and it always comes down to them using either a heat gun or torch. It’s very easy to accidentally overheat your resin and cause it to fuse to the silicone. If your resin isn’t too moisture sensitive, an alternative is to use the CO2 from your breath. If you aren’t using a respirator you can use a straw to direct your breath, otherwise positioning your cup under the exhaust part of your respirator and breathing out strongly can also work. It’s best to give your resin a slight mix after doing this to avoid amine blush from the moisture. Another alternative is to pop larger surface bubbles with a toothpick or pin, wiping it between each attempt to keep it pointy enough.

Option 3- Ultrasonic jewellery cleaner

The next option costs a little bit of money, but is generally pretty affordable. Ultrasonic jewellery cleaners use a piezoelectric plate to agitate water in the chamber above. Usually you would place an object into the water and it wears away any surface contaminants, but instead we’re gonna place a cup of resin inside and use it to force bubbles out. You simply place your mixed resin cup into the top and fill water in to the rest of the chamber until it’s as high as the resin is, but not too close to the top of the cup (water and resin don’t mix!). You then turn on the machine and the piezoelectric waves force bubbles to rise up out of the resin. I find it also removes some of the dissolved air which is pretty cool, but this method is limited by the size of the chamber so is generally only good for small to medium projects. You do have to be careful if you’re using a faster setting resin as this will speed up the cure time too. Ultrasonic jewellery cleaners range in price quite a lot, I just have a cheapish one and it works fine. If you keep an eye out you can sometimes get them second-hand pretty cheap too.

Photo of a small ultrasonic jewellery cleaner — My ultrasonic jewellery cleaner. I was lucky and found one second hand

Option 4- Vacuum chamber

Going further up the cost scale, the next option is to use a vacuum chamber. Vacuum chambers for resin generally consist of a pot with an acrylic lid connected to a vacuum pump. They work by sucking out all of the air in the chamber around the cup, and once that’s gone it then starts to force out all of the air in the resin too. They’re also good for removing air from bubbly inclusions as it will pull the air out and replace it with resin. I’ve only used mine with my thin casting resin which it works great on, but it might be more difficult to use it on a thicker or fast setting resin as when I tried it with my silicone (which had a much higher viscosity) it took longer to get all of the bubbles out. Vacuum chambers are a relatively safe piece of equipment as long as you haven’t cut too many corners, as in the unlikely event of catastrophic failure they would implode rather than explode. There are lots of guides for making one yourself if you have the tools and space to do that, or you can also buy them ready made.

Photo of a vacuum pump and a chamber made from a cooking pot with an acrylic lid — My homemade vacuum chamber setup. I got a cheap second-hand pump and cooking pot to keep costs down

Option 5- Pressure pot

The last major option is to cure your pieces in a pressure pot. This is what professional casters generally use as it can basically guarantee you a bubble free cast. A pressure pot is essentially the opposite of a vacuum chamber- instead of taking all of the air out, it forces air into the pot resulting in a high pressure within it. This pressure causes the bubbles to shrink so small that they can no longer be seen by the human eye, making casts appear to be bubble free. Pressure pots for resin casting are made by modifying paint pressure pots so you’ll generally need some technical understanding, though there are a lot of good tutorials out there to help walk you through the process. There are a few that you can buy already modified but these aren’t available in every country and will generally be quite a bit more expensive. They also require a compressor to work as this is what puts the pressurized air into the pot. Note that a pressure cooker isn’t the same thing- they work by steam and can’t safely operate to a high enough psi to be useful for resin.

Pressure pots are the most dangerous option on this list, as in a worst case scenario they explode, but as long as you’re not trying to fill it past the pressure it’s designed to handle it will generally be pretty safe. They have safety release valves which prevent the pot from going past the safe operating psi, and many people add 2 of these in case one fails, so they can be a great tool as long as you’re smart about it. The use of a pressure pot generally means you won’t have to worry about using any of the other techniques or equipment in this list as the pot will take care of it, though warming the resin beforehand can still be useful as it makes it easier to mix. The main limitation to a pressure pot is the size, they aren’t useful for every circumstance as large projects such as river tables will obviously not fit inside.

Final useful tidbits & troubleshooting

-Vibration can work similarly to an ultrasonic jewellery cleaner as it helps bubbles rise to the top. Some suggestions I’ve seen for this include placing your moulds on top of a washing machine while it’s in the spin cycle, using a vibration table, or anything else you have around the home such as an old electric toothbrush or back massager
-If you get very large bubbles that definitely weren’t there when you put the resin into your mould, it’s most likely from your resin overheating and boiling. Make sure to not pour past the recommended pour depth of your resin, and instead pour in several layers if your mould is too large.
-Small bubbles stuck to the surface of inclusions or your moulds can be coaxed out with a toothpick. It’s also a good idea to coat inclusions in resin before placing them in the mould to help cut down on bubbles
-If you’re having trouble with bubbles forming on the surface of your silicone moulds that weren’t there when you first poured the resin in, it’s most likely due to moulds that have been made with low grade silicone. You can generally tell if this is the case as they’re often more opaque than other ‘clear’ silicone moulds, more likely to have a bunch of surface imperfections, and may have a strange smell to them
-If your resin completely foams up with bubbles for no apparent reason, it’s most likely that your resin is moisture sensitive and you’ve added a colourant or inclusion that has water in it. Lots of dyes or paints are water based so it’s best to check what the base is made from before using it with resin. Some safe things to use instead include alcohol inks, resin dyes, mica or other powdered colourants

If you have any other suggestions or need any help, feel free to leave a comment down below