Hi Stephen,
The subject of your enquiry touches upon one of the most convoluted areas of intellectual property law. Its called the design/copyright overlap. It is still a very unsettled area of the law. To put it bluntly no one really knows where to draw the line between copyright protection and registered design protection in Australia.
So let us try!
You design furniture. Presumably they are 2D renditions of how furniture will look. You as author own copyright in such works. So long as you do not "industrially apply" a "corresponding design" you will be able to assert copyright ownership in an infringement situation.
So far so good.
As people have touched on above, what is a good way to claim copyright? Publication is a good way although as noted below this might affect a future claim to registered design status. If you do decide to publish, internet forums, you tube videos, facebook pages, are all good ways to "date in time" your act of publication. You should also put (c) SURNAME YEAR on each image so you can rely on the presumption of copyright ownership down the track.
Now as you have only just published these you will not have been taken to have industrially applied a corresponding design so any furniture maker that copies these designs will be potentially up for infringement of your copyright.
But what if a furniture maker approaches you to make the depicted furniture? Well if you say yes and more than 50 items are made and offered to the public your right to enforce copyright is over. You will have been taken to have authorised the industrial application of the designs. That means that your only means of enforcing the terms of the licence to the furniture maker is by contract. So if the furniture maker goes bust and a phoenixes itself you could not stop the new company from making the furniture or make them pay you a royalty. Furthermore, if some third and unrelated party starts copying those goods which incorporate your design, neither yourself or the furniture maker that has licensed your designs could stop them as your only claim would be in copyright, which would be unenforceable.
Its at this point I would like to make a point. It is in situations like those stated in the paragraph above, that makes designers resort to the claim to "work of artistic craftsmanship". If a particular artistic work can be regarded as a work of artistic craftsmanship then the authors copyright does not get extinguished when it is industrially applied. This is where legal intention and practical application diverge. The intention was for the law to apply to jewelry and hand made things - pottery, glasswork etc. But because of the importance of retaining copyright, it has been argued with respect to pens, hulls of boats, night clubbing pants, which are not really works of craftsmanship.
Could the furniture designs be works of artistic craftsmanship? Probably not. Why - firstly these are 2D drawings or renditions. Unless said drawings were intended on being works of art in their own right then the drawings would be considered regular drawings which are artistic works under the copyright act, but not works of artistic craftsmanship.
What if you had made prototypes. Say you made wooden stools. If you actually made one first without drawing it, then there would be originality (not copied from something else like a drawing) in the work, and if the stool is made in a way that could be argued to be artistic then potentially a claim to artistic craftsmanship could be made in respect of the prototype stool.
To put it another way, if the furniture you design could happily sit alongside iconic furniture down at the Powerhouse Museum then you might be able to make such a claim, but if it is more likely to sit in Ikea then it is not likely you can make such a claim.
I have acted for furniture makers who have copied other companies designs precisely in this way as there was no copyright that could be asserted. A claim to artistic craftsmanship was made but strenuously denied by our client as these were cheap chairs that had no artistic quality whatsoever. The claim failed and the copied furniture is still being sold today.
What would have protected a furniture designer?
Answer is registered designs.
By far the best way of protecting yourself is to register each design, You can include multiple designs in each registered design if they have a common design element that is new and distinctive. EG the same backs and sides of lounges in 2, 3 and 4 seated configurations.
The cost of filing each design through a patent attorney would be about $1500 each. If you do them yourself the official fee is $250 for each application.
If this is too much still, there is another, much more riskier option.
You can publish the designs on a website like facebook as an invitation for others to licence your designs. Then once you have obtained interest, you can seek to register the relevant design as a registered design.
But doesn't a application for a registered design need to be for new designs only? Yes that is true. Once a design has been published and is part of the public domain it is not regarded as new and should be unregisterable.
This is where s18 of the Designs Act comes in. This section was designed to operate to allow artistic work owners to publish their artistic work then later on seek registration of product that embodies a "corresponding design".
So, a graphic artistic today who makes a painting using a particular array of colours and shapes can register a design for a dress that has that same pattern and colours. Or someone that makes a cartoon comic and decides later on to make a Tshirt featuring the cartoon image. That was the intention of the section. Where an artistic work is interpreted into a new product. It was not intended on covering the 2D works of products that are then made in 3D. But because it has been worded quite widely, and by reference to the same concept of "corresponding design", there does appear to be room for there to be included within the section, 2D drawings to 3D products.
This is where there is a real confusion in the reported decisions. In cases on s18 they said its not a "corresponding design" if it is the same design that is sought to be registered as what is depicted in the earlier artistic work. For example, one case involved a part for a water slide, and the drawing for it was the same drawing that was subsequently sought to be registered. The court in that case said its not a corresponding design, it is the same design ie 2D to 3D.
The reason why these cases are not particularly compelling is that the opposite is found when s77 of the copyright act is considered when seeking to extinguish copyright because of the industrial application of a corresponding design. The acts state they are to have the same meaning but the Courts are applying them differently.
So if you do publish your designs and then seek to register them later you would best be advised to at least use different drawings and not seek to register the same drawings as the artistic works. I would probably also put a lot of people and soft furnishings in the original artistic works to reduce the chance of someone saying that the artistic work was merely the plans for the product.
This is a risky strategy, relying on s18 of the Designs Act. It would be much preferable to register your designs as registered designs prior to publication. Appeals to s18 rarely if ever have gotten up. But it does represent a legal argument that could be made just in case you happen to design the next Eames chair.
If all of that has left your head shaking, fear not, that's how most of us feel practicing in this area. Its horribly complex and there is no clear answer either way. It will take multiple $500K lawsuits to settle this area and that is not going to happen soon.
So good luck with it all.
Cheers
Len