I had begun to gather articles about making Neandertal birch glue. And I finally stumbled upon a paper that does just that (for the scientific part) and describes the only experiment - that I have found till now - describing convincing results. There is also a bibliography, but unfortunately for most of us, it is mainly in Polish. There are interesting photos, and I would have loved seeing how was the glue accumulated at the bottom of the kiln, before its removal. The species of birch used in the experiment remains unknown.
A Method of Wood Tar Production, Without the Use of Ceramics
Grzegorz Osipowicz ; Reconstr. Exp. Archaeology EuroREA, 01/2005; 2:11-17.
Synthesis : http://www.keap.umk.pl/en/making-birch-tar-without-use-of-ceramics.html
Details : https://www.researchgate.net/publication/259583450_A_method_of_wood_tar_production_without_the_use_of_ceramics
Remarks, other links and other experiments
[no correct citations : a bunch of keywords, extracts and links]
From the above paper, we can guess that one primitive way of making glue from birch bark is not by producing tar first. In the described process, the tar mixes itself with charcoal : by "contamination" with carbonized birch bark.
There are conflicting evaluations about the age of the piece of birch glue found at Königsaue : 40 000 years old or 80 000 years old. Older pieces of birch tar have been found in Italy (Campitello) : some say they are 200000 years old, others say that it's dubbious (see http://www.thesubversivearchaeologist.com/2012/02/of-birch-tar-hafts-and-caribou-fleshers.html).
From a short synthesis about the use of adhesives in Africa and Europe :
Still unclear to us ignorants... because we can read such different things here and there : Does the tar simply drip down, exuded in liquid form by the bark without going through a vaporized / gaseous state ? or does it condense itself from vaporized compounds ? or does it do both things, at various places in the kiln and at various stages of the process, depending on the temperature ?
Other apparently confusing elements :
"dry distillation", "destructive wood distillation", 300-400C, 340-400 °C, 220-280 °C, over 650°F [343°C], "released vapour is collected by a method which cools it down" , "wood tar is acquired during firing by it running through the holes into the smaller vessel placed underneath the big one" , "Without an airtight firing chamber, the wood tar would either evaporate or [...]", "limited air supply", Betula pendula Roth., Betula pubescens, ...
Much simpler techniques than "dry distillation" ?
"in simple covered pits (Pawlik 2004) or underneath stones
inside a fire (Palmer 2007). It may even be possible through holding
bark tightly wrapped around a stick inside the heart of a fire (Knul,
pers. comm. 2011)".
As technologically simple as traditional charcoal making ?
"[about (the very primitive) charcoal making in the XIX-XX in Itlay; page 35] the production of pitch was one of the secondary activities related to the making of charcoal (it was employed for covering roofs, or as a glue for tools, and the carbonai used to sell it together with charcoal"
Links and Experiments :
Grzegorz Osipowicz continues to experiment, and tries different types of kilns
Neanderthal Superglue [2013; video]
Shows a primitive process which result - after 8 hours of burning - is a very faint layer of tar on a small stone; no liquid.
Neanderthals 'used glue to make tools' ; Saturday, 19 January, 2002, 08:00 GMT
Keywords : Dr Dietrich Mania; Germany; Königsaue; Harz Mountains; Friedrich-Schiller University ; European Journal of Archaeology
"A sticky fingerprint on a fossilised blob of wood"
keywords : Aschersleben; Harz Mountain; Heinrich Wunderlich; Professor Dietrich Mania of Freidrich-Schiller University in Jena ; more than 80 000 years old
Neanderthals Clever Enough To Make 'Superglue'
Extract :"The research, carried out at the Doerner-Institut in Munich, found the pitch was a birch pitch, which can be only be produced at temperatures of 300-400C"
keywords : Discovered in a lignite mining pit in the Harz mountains in Germany. Professor Chris Stringer, Natural History Museum in London. Professor Dietrich Mania of Freidrich-Schiller University in Jena
High-Tech in the Middle Palaeolithic: Neandertal-Manufactured Pitch Identified
European journal of archaelogy
keywords : Johann Koller,Ursula Baumer Doerner-Institut, München, Germany; Dietrich Mania , Friedrich-Schiller-Universität Jena, Germany
Neanderthals Defy Stereotypes
By Evan Hadingham ; Posted 01.09.13; NOVA
Extracts : [...] distilling pitch from birch bark requires an oxygen-free environment and sustained temperatures of over 650° F [...] first discovery was made in 1963 at Kínigsaue, in then-East Germany. [...] Two small, hardened lumps of black material were found [...] one bearing a fingerprint and the other the impression of a wooden haft or handle. [...] In 2001, the lumps were dated to at least 40,000 years ago [...] birch bark pitch produced by the dry distillation process. Much older evidence was found at the Campitello quarry in central Italy. [...] two large lumps of black pitch, which covered the end of two stone flakes crafted in a typical Neanderthal style. The Campitello find dates back over 200,000 years [...] A third Neanderthal site at Inden-Altdorf, overlooking the Inde River in Germany and dating to around 128,000 to 115,000 years ago, features more than 80 stone tools flecked with black material, but the chemical analysis indicating that this was distilled pitch requires further confirmation.
[...] the team proposed that the Neanderthals had invented the following procedure: first, wrap a long strip of birch bark around a small pebble so that it forms a cigar-shaped roll. Next, dig a narrow pit, then set light to one end of the roll and place the burning end at the bottom of the pit. In the confined space at the bottom of the pit, the smoldering bark quickly uses up oxygen and causes the pitch to "sweat," or condense, out of the roll of bark onto the surface of the pebble. While still hot, the pitch is a sticky liquid that can be used immediately as glue.
[...] Although German experimental archaeologist Friedrich Palmer succeeded in earlier published experiments, in the NOVA program, he fails to produce more than a thin smear of pitch. In 2010, another team reported success by a variation on the technique: lay strips of bark on a flat stone surface, cover them with a couple of inches of sand to exclude oxygen, then build a fire on top. After a little over an hour, the team dug up the stone and found that enough pitch had dripped onto its surface to haft two or three spears or tools.However, the team succeeded easily on their first attempt only because they had a thermometer to judge if the fire was hot enough.[...] Archaeologist Wil Roebroeks, who witnessed Palmer's NOVA experiment, comments that its failure underscores the complexity of the process,[...]
Sticking with Neanderthals: Identifying Neanderthal Mastics and their Signatures
Joseph Walsh; Advisor: Bruce Hardy, PhD., David Heithaus
Ça colle pour l'homme de Neandertal
Par Sylvie BRIET — 22 janvier 2002 à 21:45
Extracts : [... ] En 1963, Dietrich Mania, paléontologue à l'université d'Iéna, découvre des outils et morceaux de poix datant de l'époque de Neandertal dans une carrière de lignite au nord-est des montagnes du Harz, près de Königsaue (Allemagne).[...] L'un des morceaux comporte une empreinte de doigt mais également la marque d'une lame de silex et celles de cellules de bois: ce morceau de poix, utilisé comme adhésif, fixait un manche en bois à une lame de couteau en silex. Tout le matériel découvert (comprenant d'autres pièces de bois et outils en silex) fut transféré au Landesmuseum à Halle. Sans être analysé plus avant car les techniques n'existaient pas.Trente-trois ans plus tard, le matériel est envoyé à l'institut Doerner. Des premiers résultats furent publiés en 1999. Cette fois, Johann Koller et Ursula Baumer ont établi la composition chimique [...] origine biologique [...] découvert que le niveau de bétulin (Betula verrucosa) est très élevé dans leurs morceaux de poix, comme dans l'écorce de bois de bouleau. [...] pour fabriquer une glue de cette qualité, il a fallu chauffer l'écorce dans une fourchette de température très étroite: entre 340 et 400 °C. [...] L'abondance du matériel annexe, les outils multiples suggèrent qu'il existe deux cultures sur ce site. L'une d'elles peut être attribuée aux premiers Homo sapiens modernes, la seconde revient clairement aux Néandertaliens. Restent des incertitudes sur les datations. Dietrich Mania, le paléontologue qui a découvert le site, n'a aucun doute sur l'âge des couches géologiques qui datent de 80 000 ans. Les morceaux ont été envoyés à Oxford (Grande-Bretagne) pour une datation au radiocarbone qui a donné 44 000 et 48 000 ans! La trop faible concentration en carbone pourrait expliquer cette différence et les chercheurs penchent pour la date géologique. [...]
European Journal of Archaeology de décembre 2001.
Neanderthal Glue Makers
[Video, 2008, National Geograhics]
Claims to have a good idea of how Neandertals could have made glue from birch bark.
Illustrates the first steps, but doesn't show the end of the process nor success.
Evokes Native American Tribe in Canada having an ancestral technique for that, but doesn't name it, unfortunately...
keywords : Museum of Halle; fragment of ice age adhesive found in the 1960 in Königsaue in eastern germany; Dr Christian Heinrich Wunderlich, "no scientist has succeeded in making this pitch glue with the material Neandertals could have used"
Genotoxicity Assessment of Birch-Bark Tar—A Most Versatile Prehistoric Adhesive
Extract: "heating (pyrolysis) the bark of birch trees (e.g. European white birch Betula pendula Roth) under reducing conditions with limited air supply and a temperature of over 300˚C, the distillation product is an odorous dark-brown viscous pitch (Dudd & Evershed, 1999)."
Experimental explorations into the aceramic dry distillation of Betula pubescens (downy birch) bark tar.
First online: 21 June 2013.Peter Groom,Tine Schenck,Grethe Moéll Pedersen
Extract : "[...] Though the experiments did not successfully produce tar as a finished product, they did lead to a better understanding of the dry distillation process [...]"
Traditional Glue, Adhesive and Poison Used for Composite Weapons by Ju/’hoan San in Nyae Nyae, Namibia. Implications for the Evolution of Hunting Equipment in Prehistory
Lyn Wadley , Gary Trower , Lucinda Backwell , Francesco d’Errico
PLOS; Published: October 28, 2015; DOI: 10.1371/journal.pone.0140269
Extract : "Western European Neanderthals heated birch bark for glue by Marine Isotope Stage 6 (MIS 6, that is, ~200,000–130,000 years ago) at the Campitello quarry site in Central Italy [1,2]. Stone tools from an occupation ~120,000 (120 ka) years old, in Inden-Altdorf, Germany, were hafted with birch bark pitch  and it was also discovered at Königsaue, Germany, where the geological-stratigraphic context suggests ages older than 80 ka ."
And here are my own experiments, not all failed
Using Organic Materials in prehistory
Universtity College of London
[not about Neandertals] Werner Pfeifer describes an open distillation process and a closed distillation process; in both cases there are similarities with the kiln of Grzegorz Osipowicz ; but the result is very different : liquid tar, not hard glue.
Wood Tar in The Dnieper and Elbe Communities - VI-II Millenium BC
Slavomir Pietrzak; Baltic-Pontic studies; 2012
[not about Neandertals]
When did humans learn to boil ?
John D. Speth, 2014
Humans may have, very early, boiled their food in skins, paunches, bark containers, by direct heating over a flame (without using heated stones, nor ceramic vessels). These techniques have been described in a number of Native American cultures. [see pages 57 to 59, in "Boiling in perishable containers without using heated stones"].
About birch glue :
"Birch tar can only be produced by a process of destructive (dry) distillation, in the absence of oxygen, and with temperatures maintained for several hours between a minimum of 340 ºC and a maximum of about 400 ºC (Koller et al. 2001; Peters et al. 2005: 335–337). [...] No one to my knowledge has yet adequately figured out how Neanderthals would have accomplished this complex feat of pyrotechnics without the aid of metal or ceramic containers (see Osipowicz 2005; Peters et al. 2005: 336–337; Palmer 2007; Meijer and Pomstra 2011; Groom et al. 2015)." [[what ? Osipowicz shows a way to do it, actually]]
The bibliograhy related to these extracts :
Groom, P., Schenck, T., Moéll Pedersen, G. 2015. Experimental explorations into the aceramic dry distillation of Betula pubescens (downy birch) bark tar. Archaeological and Anthropological Sciences 7, 47–58.
Koller, J., Baumer, U., Mania, D. 2001. High-tech in the Middle Palaeolithic: Neandertal-manufactured pitch identified. European Journal of Archaeology 4, 385–397.
Meijer, R., Pomstra, D. 2011. The production of birch pitch with hunter-gatherer technology: a possibility. Experimentelle Archäologie in Europa, Bilanz 2011, 199-204.
Osipowicz, G. 2005. A method of wood tar production, without the use of ceramics. euroREA 2, 11–17.
Palmer, F. 2007. Die entstehung von birkenpech in einer feuerstelle unter Paläolithischen bedingungen. Mitteilungen der Gesellschaft für Urgeschichte 16, 75–83.
Peters, K.E., Walters, C.C., Moldowan, J.M. 2005. The Biomarker Guide, Vol. 1. Biomarkers and Isotopes in the Environment and Human History. 2nd edition. Cambridge University Press, Cambridge.