In a remarkable bit of serendipity I found a very useful video on YouTube yesterday (serendipitous because I was merely browsing and not looking for anything on this subject and the video was posted only 4 days ago). The channel is produced by someone who has rescued and repaired a scanning electron microscope and in this video he produces gold nanoparticles as a calibration target for his imaging.
Aside from the fact that we could have saved him a great deal of time trouble and money by directing him to Bostick and Sullivan to buy a $12 bottle of gold chloride solution rather than having to make his own from a gold ingot - he researches ways to create nanoparticles (of gold) at different sizes, by using different temperatures. He also introduces two reducing agents - citrate, and bisulphate, both of which should be accessible. He doesn't consider other capping agents like PVP.
Thank you so much for all your testing and sharing! The homemade Polaroid is truly beyond imagination.
If I may, I'd like to share a small note. Having published some papers on metal nanoparticles, I can say that the synthesis of gold, silver, platinum, or palladium nanoparticles is relatively simple. The main challenge often lies in discovering unknown methods. However, replicating reported methods typically just need some kitchen equipment. Many people here are doing similar things when they develop B/W films or use gold toning solutions. Essentially, they can control the formation of silver and gold nanoparticles.
To quickly acquire relevant knowledge, I suggest searching for the desired topic on Google Scholar. For example, searching for "Size Control of Palladium Nanoparticles" can lead you to research papers such as "Chen, Hongjun, et al. 'Synthesis of palladium nanoparticles and their applications for surface-enhanced Raman scattering and electrocatalysis.' The Journal of Physical Chemistry C 114.50 (2010): 21976-21981." or "Wang, Ying, et al. 'Size-controlled synthesis of palladium nanoparticles.' Journal of Dispersion Science and Technology 29.6 (2008): 891-894." These papers contain more methods and results that researchers have tried, as well as analyses of factors influencing the growth process. Reading them or following their methods is often simpler than mixing own C41 developer and make it work.
For example, if you need palladium nanoparticles with diameters between 25 and 100 nm, a paper says:"
100 ml of solution containing 0.01 g HAuCl4·3H2O was brought to reflux and 3 ml 1% sodium citrate solution was added while stirring. The boiling solution was then kept for another 40 min and left to cool to room temperature. The resulting gold sol contains 12 nm particles according to TEM.
The preparation of Pd nanoparticles was as follows. Six solutions (A–F) containing 10 ml 1.0 mM H2PdCl4 and a varied amount of 12 nm gold seeds (4, 3, 2, 1, 0.5 or 0.1 ml of solution), respectively, were prepared. Next, an excess amount of ascorbic acid (100 mM, 1.2 ml) was added to the above solutions while stirring. The red color of the gold sol changed to a dark brown color of palladium colloids, suggesting the formation of palladium nanoparticles. Throughout the experiment was kept at room temperature. ", From Lu, Lehui, et al. "Improved size control of large palladium nanoparticles by a seeding growth method."
Journal of Materials Chemistry 12.2 (2002): 156-158.