Confused!

Need some advice- after reading through many posts I had myself convinced to buy a pressure pot and compressor to have a go at casting, but then I read that many are casting polyester without pressure? Can I cast polyester coloured with powders without pressure pot?


I would really like to make some hybrids which brings me to my next question - Do all woods require stabilising before casting? (I want to buy some nice pieces of burl)

Any advice would be appreciated before I shell out a load of cash. Thanks

Hi, you can certainly cast polyester resin without vacuum or pressure, including when using mica powders, etc.

With regards to hybrid blanks, yes you can cast unstablised wood with resin - however, there are other issues to consider.

Firstly, I don't believe that polyester resin forms a great bond with wood, stabilised or unstablised - polyester resin shrinks when cast, so it may shrink away from the wood. That said, I've never actually tried it, so there may well be someone on here who has successfully done it (a pressure pot may help).

If you decided to use a different resin to get away from the shrinkage issue, then there are further things to think about.

Polyurethane doesn't play nicely with water, so you would have to make sure any wood was bone dry. Also, wood will introduce lots of air into the mix, so you would probably need to use pressure to get rid of these bubbles. You could try giving the wood a coat of resin before casting it, and letting it dry to form a seal around the wood, but it would be messy and I'm not sure how it would actually work in practise.

You could also cast wood with epoxy resin, which is much more forgiving in terms of moisture, and which also usually degasses itself fairly well - provided you use one with a long open time. The downside with epoxy is that it does take a long time to set, and generally isn't a preferred resin to turn as it doesn't hold up to heat particularly well, which can make it difficult to polish up.

fingwe said:

Hi, you can certainly cast polyester resin without vacuum or pressure, including when using mica powders, etc.

With regards to hybrid blanks, yes you can cast unstablised wood with resin - however, there are other issues to consider.

Firstly, I don't believe that polyester resin forms a great bond with wood, stabilised or unstablised - polyester resin shrinks when cast, so it may shrink away from the wood. That said, I've never actually tried it, so there may well be someone on here who has successfully done it (a pressure pot may help).

If you decided to use a different resin to get away from the shrinkage issue, then there are further things to think about.

Polyurethane doesn't play nicely with water, so you would have to make sure any wood was bone dry. Also, wood will introduce lots of air into the mix, so you would probably need to use pressure to get rid of these bubbles. You could try giving the wood a coat of resin before casting it, and letting it dry to form a seal around the wood, but it would be messy and I'm not sure how it would actually work in practise.

You could also cast wood with epoxy resin, which is much more forgiving in terms of moisture, and which also usually degasses itself fairly well - provided you use one with a long open time. The downside with epoxy is that it does take a long time to set, and generally isn't a preferred resin to turn as it doesn't hold up to heat particularly well, which can make it difficult to polish up.

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I was wondering if the timber part was stabilised first would that make the process easier. I have a mate who reduces all of his prized wood for knife makers to as near zero as he can then stabilise. His product is in world demand.

Peter........................PS it would appear knife makers are prepared to pay the needed high costs.In penmaking it would seem prohibitive.

Yes, it's generally preferred to stabilise wood before casting, but not absolutely essential.

fingwe said:

Hi, you can certainly cast polyester resin without vacuum or pressure, including when using mica powders, etc.

With regards to hybrid blanks, yes you can cast unstablised wood with resin - however, there are other issues to consider.

Firstly, I don't believe that polyester resin forms a great bond with wood, stabilised or unstablised - polyester resin shrinks when cast, so it may shrink away from the wood. That said, I've never actually tried it, so there may well be someone on here who has successfully done it (a pressure pot may help).

If you decided to use a different resin to get away from the shrinkage issue, then there are further things to think about.

Polyurethane doesn't play nicely with water, so you would have to make sure any wood was bone dry. Also, wood will introduce lots of air into the mix, so you would probably need to use pressure to get rid of these bubbles. You could try giving the wood a coat of resin before casting it, and letting it dry to form a seal around the wood, but it would be messy and I'm not sure how it would actually work in practise.

You could also cast wood with epoxy resin, which is much more forgiving in terms of moisture, and which also usually degasses itself fairly well - provided you use one with a long open time. The downside with epoxy is that it does take a long time to set, and generally isn't a preferred resin to turn as it doesn't hold up to heat particularly well, which can make it difficult to polish up.

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What an asset to this forum you are Melanie. I am also one who suffers from a vast lack of knowledge and confusion in regard to casting, and not for the first time on varying topics you have cut straight to the point, in clear, readable terms, without the use of confusing abbreviations, to give an answer that debunks many of the mysteries. - Thank you.

Thanks for the advice Melanie.

Phil, thanks very much! I won't claim to know everything there is to know about resin casting and I'm sure that there are many on here who have been doing it a lot longer than me. However, with wanting to do several different things with resin (cast pen blanks, cast jewellery blanks, cast various things in pen and jewellery blanks, including wood), I've done lots of research and a fair bit of experimentation.

Unfortunately, I've found that there is no perfect resin, each one has it's own drawbacks and limitations.

Polyester is by far the cheapest. It's also one of the easiest resins to use as it doesn't require pressure or vacuum, nor a narrow temperature range to set in. The downside with it is it's really strong smell (I don't find the smell too unpleasant, it's just overwhelming if you don't have good ventilation) and the fact that it is very brittle and hence not very strong. The brittleness is a deal breaker for me, as the dip pens I make have no internal structure, so the strength of the resin is imperative.

Epoxy resin is another easy to use resin. It's a lot stronger than polyester, is usually water clear and generally doesn't need pressure or vacuum - though this isn't always the case (I'm currently using a fairly fast setting one (we're talking about a 30 minute work time, but still around a day to fully set) and that will be full of tiny bubbles if I don't degass). It is also usually fairly forgiving of temperature. The downsides are that it needs really good mixing (not a big issue, but it makes my hand ache), is a LOT more expensive than polyester resin and can be difficult to polish up if you use a method which generates a fair amount of heat - and regardless, it will never polish up as nicely as a commercially made acrylic blank. It will also have a tendency to distort of you generate a lot of heat whilst turning. It also generally takes at least a day to set, and it may be several days until you can actually work it with power tools. This slow setting time can also be an issue if you wanted to suspend anything within the resin - mica powder is generally OK, but something like glitter would sink to the bottom.

Polyurethane is generally the preferred resin for making woodturning blanks, but again, it has drawbacks. There are also differences, depending on whether you want waterclear resin, or opaque resin.

I'll address waterclear polyurethane first...if you want a waterclear resin, it is expensive - around the same cost as epoxy. Secondly, the fumes given off by the waterclear polyurethane resins are toxic, so even though you can't smell them, you really need to work in a very well ventilated area, or wear breathing apparatus. Thirdly, it is very picky about the conditions in which it will set. Each different resin varies, but generally it has a very narrow temperature window (usually around 22-25 degrees) and will only set in certain types of mould - polypropylene (the type of stuff many chopping boards are made out of), or addition cured silicone are generally recommended. Fourthly, despite what the manufacturers may tell you, if you want bubble free castings, you will almost always need to use either vacuum or pressure - note that if you're making your castings opaque with something like mica powder this might not apply, as the bubbles are tiny....but if you want a totally clear casting, you'll need to get rid of them. Finally, and probably my main issue with polyurethane waterclear, is that I have yet to find one which polishes up well. Yes, you can polish it, but you will never get the glass like finish you can get from commercially made acrylic blanks. The benefits of polyurethane are that is generally sets pretty quickly (there are lots of different resins out there with different setting times, so it's fairly easy to find one which suits you), is strong, and turns pretty well (like epoxy, it will distort with heat, but is a little more forgiving).

Opaque polyurethane is generally about half the price of waterclear, and is usually more forgiving and easier to cast. It generally has a much shorter working time (2 minutes is not uncommon), and you may be able to get away without vacuum/pressure (there will be tiny bubbles in there, but they're generally not as noticeable in opaque resin). Because of it's shorter working time, it can be difficult to make multicoloured blanks, as you can't get them all mixed in time, however, there are a couple with longer working times if this is important to you. You also can't use pearly mica powders in the opaque resins. Well, you can, but they only give a light colour, you won't get the shimmery, pearly effects. The opaque polyurethanes are generally a lot softer than the waterclear polyurethanes, and you will find they distort at high temperatures. However, they are lovely to turn, and do polish up very nicely - probably the nicest of all the casting resins.

Bottom line is, you need to decide what factors are important to you, and choose which resin to use accordingly. Some of the issues I've highlighted might not be an issue to you - such as the resin distorting at high temperatures. As I've said before, I make dip pens with no internal support structure, so if a resin distorts whilst I'm turning it, it's a big issue. When turned on a pen tube it probably isn't an issue at all.

And as always, these are my experiences, your mileage may vary

......and there it is. A concise yet comprehensive summary of the things that some of us (read, me in particular) have been trying to get our heads around for ages. I'll tell you anything you want to know about nibs and refills, but casting - No!

Brilliant - Thank you so much.

No problem....casting is one of my favourite parts of penmaking, but there can be lots of frustrations along the way.

Thanks Melanie for the pictures you have painted re casting in my mind, clarified many thoughts.

Peter.