The worker's or maker's mark was first instituted in England by the statute of 1363 (see REFERENCE 1) which ordered that every Master Goldsmith should have a mark of his own, known to those appointed by the King to survey their work. In chronological order the maker's mark was the second marks becoming compulsory, after the introduction of the crowned leopard head (see REFERENCE 2) in force since 1300, that was the guarantee given by the Worshipful Company of Goldsmiths that the silver was at list of sterling standard (925 parts of silver per 1000 parts of alloy).
The maker's mark should then allow uniquely identifying the silversmith, but this can be difficult when registered marks of different silversmiths are similar and the period of their activity overlaps.
This is the case of a maker's marks, RR pellet between (R•R), struck on many silver salvers of the second half of the XVIII century, that can be attributed to Richard Rugg or to Robert Rew. Both are considered to have been prolific salver makers and they worked approximately in the same period.
The problem of the correct attribution of the R•R mark, is well known and it is not a case that it compared in a rhyme in the introduction to a Sotheby's catalogue of provincial silver spoons, offered for sale in 1935 (see NOTE 1)):

Arthur Grimwade (see REFERENCE 3) offered a solution to this dilemma in 1976, noting that the similar marks of the two silversmiths were of different size and, in the case of Richard Rugg, on punch of different shape (Figure 1, marks n. 2420, 2421and 2422). In the biography of both Richard Rugg and Robert Rew, Grimwade says: "It has in the past been considered impossible to distinguish between the marks of Rugg and Robert Rew. The size of the only similar mark (my note: R•R in a rectangular punch) which each entered in, however, so widely different from the other that there need to be no doubt in the matter".

Figure 1 – "RR" marks registered at the Goldsmith’s Hall, according to Grimwade (see REFERENCE 1). The reproduction of the marks should takes account of their difference in size

Referring to marks struck on salvers, a possible confusion in the attribution can occur only with marks n. 2420 and 2422, for the period between 1754 and 1775. At the latter date Richard Rugg registered another marks (n. 2421) with a bilobed punch. The other two similar marks (n. 2423 and 2424) refer to smallworker (see NOTE 2) and it would be very hard for them to produce salvers, a particular branch among the category of largeworker (see NOTE 3) for specialist in cast works ((see NOTE 4).

But is the question really closed?

Time ago I came across a salver hallmarked for London 1771 and bearing the maker’s marks RR unpelleted. Who was the maker of this salver? Neither Richard Rugg nor Robert Rew registered a similar mark, or at least, according to Grimwade, there is no record for this at the Goldsmiths' Hall.
The only silversmith to which a similar mark could be attributed is Richard Redrick. His working activity overlaps those of Rugg and Rew, but, as already said, he was a smallworker and then should be excluded.
So, I started a more accurate research, including bibliographic references written before the Grimwade work.

Wilfred Joseph Cripps in his "Old English Plate: ecclesiastical, decorative, and domestic: its makers and marks "(see REFERENCE 4), first published in 1878, reported the marks showed in Figure 2.

Figure 2 - Richard Rugg and Robert Rew marks reported by Cripps (see REFERENCE 4) on the base of the observation of real hallmarks struck on silver plate

Cripps attributed a big RR unpelleted mark similar to that impressed on the cited salver to Robert Rew, stating that the R•R (pellet between) mark that he attributed to Richard Rugg is of smaller dimension. Cripps has only worked on the base of hallmarks struck on real examples of plate, so it is not clear why he has come to this conclusion. No trace of both the larger R•R pellet between Robert Rew mark and the R•R Richard Rugg mark in a bilobed punch in the work of Cripps.
William Chaffer in his work "Gilda Aurifabrorum" (see REFERENCE 5), dating 1899, reports the marks showed in Figure 3, taken from the Register of Large Plate Workers from 1739 to 1769 and in the Register of Small Workers from 1758 to 1773 and Large Workers from 1774 to 1805, held at the Goldsmiths’ Hall. Chaffer was the first person to whom was permitted the consultation of the registers kept at the Goldsmiths’ Hall and he reproduced all the marks as a facsimile (see NOTE 5).

Figure 3 – Richard Rugg and Robert Rew marks reproduced by Chaffer (see REFERENCE 5) on the base of the records found in the Register of Large Plate Workers from 30th May 1739 to 30th September 1769 and in the Register of Small Workers from 1758 to 1773 and Large Workers from 1774 to 1805, kept at the Goldsmith's Hall

The marks are matching with those independently reproduced (photostatically) by Grimwade, but the attribution is inverted, the larger one being ascribed to Richard Rugg. Furthermore Chaffer also reported the new RR Rugg mark in a bilobed punch but it is reproduced without pellet. No trace in the registers of the RR unpelleted mark, found by Cripps on a salver dating 1759.
A few years later, Montague Howard, in his "Old London silver – its history, its makers and its marks", dating 1903 (see REFERENCE 6), reported a list of maker marks, referring to Chaffer work "Gilda Aurifabrorum" (see REFERENCE 5) and the elaboration given by Cripps (see REFERENCE 4) (Figure 4).

Figure 4 – Richard Rugg and Robert Rew marks reported by Howard (see REFERENCE 4) and derived by the works of Chaffer and Cripps

The work is clearly a merge of the Cripps and Chaffer researches but, again, it is not explained why Howard has judged the work of Cripps to be more representative than that of Chaffer for the two similar RR marks in a rectangular punch, and has referred to the work of Chaffer only for the RR mark in a bilobed punch, which, like in the Chaffer work, is reproduced without pellet.
Charles J. Jackson (see REFERENCE 7) in his "English Goldsmiths and their marks - A history of the goldsmiths and plate workers of England, Scotland and Ireland", first published in 1921, reports the record of the registration of both Richard Rugg and Robert Rew in 1754 and an example of the their marks as shown in Figure 5. Jackson specifies in another section of his work that the reported marks have been found on salvers, apart the RR mark in a bilobed punch which was observed on a fish slice. No marks similar to that found on the cited salver (RR unpelleted) are shown by him in the period of activity of the two silversmiths.

Figure 5 – Richard Rugg and Robert Rew marks reported by Charles J. Jackson (see REFERENCE 7)

Jackson (like Cripps) has mainly worked on the base of real hallmarks struck on wrought plate and he came across two different salvers crafted in the same period (1760-1761 and 1761-1762 respectively), both struck with the R•R pellet between mark in a rectangular punch. The two marks had different size, and Jackson has ascribed the bigger one to Robert Rew. Again the source of this attribution it is not clear.
The RR mark in a bilobed punch found by Jackson on a fish slice and attributed to Rugg, is, like in Cripps and Montague works, reproduced unpelleted. Although it is quite unusual that Rugg has produced flatware, the date letter on this fish slice was for 1775, indicating that it was marked between May 1775 and May 1776 (see NOTE 10), after the registration of this mark by Richard Rugg in March 1775.

The only clear thing is that the historical sources are contradictory. Difficult to say where the truth lies, but it is likely that the most faithful situation is that given by Grimwade (Figure 1), who should have taken into account all the past published data. So, my research continued by collecting examples of salvers of the second half of the XVIII century struck with the maker’s mark RR. I found 65 examples of salvers dating between 1754 and 1783 bearing these marks. Figure 6 reports all the found examples ranked by date letter. We can draw the following consideration (see NOTE 6):

• between 1754 and 1769, all the found maker’s marks (R•R) are pellet between and of the same dimension (if compared with the other marks);
• between 1770 and 1774, all the found maker’s marks (RR) are of bigger dimension than that found before and unpelleted;
• since 1774 I only found examples bearing the new Richard Rugg mark (R•R pellet between in a bilobed punch);
• no example of the RR unpelleted mark in a bilobed punch was found in my survey (see NOTE 7);
• no example of the bigger R•R pellet between mark was found in my survey (see NOTE 8).

Referring to the period 1754-1769, it seems that during my research I came across only marks that, on the base of their dimension, should be attributed to Richard Rugg, as they apparently match that reported by Grimwade for this maker. This seems to be in contradiction with the common belief that both Rugg and Rew have been prolific salver makers working in the same period (since 1754). Furthermore I found the bigger RR unpelleted mark only on examples dating between 1770 and 1774, while Cripps (see REFERENCE 4) documented this mark since 1759.
Considering the record reported by Jackson (Figure 5) and an error in the work of Cripps, concerning the record of the bigger RR unpelleted mark (Figure 2) attributed to Rew (it would be pellet between), a possible explanation can be that Robert Rew produced a very few number of salver to allow that some examples could be included in my survey. In conclusion Rew was not a prolific salver maker as he is generally considered.
The only alternative would be that Robert Rew and Richard Rugg adopted, at least after 1759, very similar marks, not only the R•R pellet between mark, but also the RR unpelleted mark. It is therefore highly unlikely that both silversmiths simultaneously ceased the use of a similar mark to adopt, again, another - different - similar mark.
After a very interesting exchange of opinion with Phil Osbourn, the webmaster of the site www.silvermakersmarks.co.uk, I came at the following conclusion:

• If we consider Grimwade as the most accurate source of information, the marks found in my survey on salver dating between 1754 and 1769, match that of Rugg's (n. 2420) and it is not to be excluded that all the pre 1770 examples reported in Figure 5 have been made by Rugg. If this is correct there is the evidence that Rew produced only a very few number of salver to appear in my survey.
• About the larger RR mark, it may not really be unregistered as it would have been in the missing largeworkers' register for the period 1758 to 1773 (see NOTE 9). It seems too coincidental that the small R•R mark disappears from use, immediately followed by the appearance of the larger RR unpelleted mark for them not to have been those of the same silversmith.
• The fact I found salvers with the same date letter T for 1774/75 bearing either the RR unpelleted or the R•R bilobed marks, could be not a contradiction because the date letter usually changed in May each year (see NOTE 10). The changeover by Rugg from a large unpelleted RR to a bilobed R•R can be, chronologically: • larger unpelleted RR mark from May-June 1774 to March 1775; • bilobed R•R mark from its registration in March 1775 to May 1775.

So, was Rew really a prolific salver maker or is this just a symptom of the documented historical confusion between the two silversmiths?
Apart the found evidences some questions are still open:

• there is no evidence that the bigger unpelleted RR mark was effectively registered and, if so, either by Richard Rugg or Robert Rew, being the register missing;
• one can argue that the hypothesis of the mark reported in the missing register 1758-1773 can also be consistent with the RR unpelleted mark reported by Cripps (see REFERENCE 4) on a salver dating 1759 and, if so, the attribution of this mark to Robert Rew would be more likely;
• it is a matter of fact that I did not found any example of the bigger R•R pellet between mark in my research and the only record available for it is that reported by Jackson (Figure 5), and in principle we cannot exclude that the error was done by Jackson and not by Cripps in the documentation of the bigger RR mark, and that this mark was really unpelleted.

Another question that can arise is: does the bigger R•R pellet between mark really exist? Phil, reports in his website a mark R•R found on a sauce boat dating 1761 that can match with the Robert Rew registered mark n. 2422 (see REFERENCE 8). But can this mark unequivocally be attributed to Robert Rew? Grimwade (see REFERENCE 3) reports that Richard Redrick used similar marks (R•R pellet between) since 1763, and a sauce boat is little enough to be produced by a smallworker as Redrick was.
This sauce boat bears the date letter F for 1761/62 when Redrick was still using an unpelleted RR mark and the conclusion should be that no R•R marks could be used at this date by him and then can really be attributed to Robert Rew. But, again, the historical sources do not help us: Jackson (see REFERENCE 7) in the chapter "Chronological list of names of London Goldsmiths" of his "English Goldsmiths and their marks" warns to be careful with the date of registration of marks because they may have been in use one of two years before registration.
Furthermore, the change of a mark by a silversmith is usually related to the passage of business from father to son, but Rugg had only one son (who was apprentice to him) and then why he changed two marks in a so short period of time?
As reported by the cited rhyme in the introduction to the Sotheby's catalogue "the question is left still in doubt" and the debate on the correct attribution of RR mark, both pellet between and unpelleted, is still open for discussion.

REFERENCES

(1) Act 28 of Edward I. c. 20.
(2) Statute 37 Edward III. c. 7.
(3) Arthur G. Grimwade, 1976. "London goldsmiths 1697-1837: Their marks and lives - from the original registers at Goldsmiths' Hall and other sources", Faber & Faber, Limited , London.
(4) Wilfred Joseph Cripps, 1894. "Old English Plate: ecclesiastical, decorative, and domestic: its makers and marks", 5th. ed., rev. and enl., J. Murray, London
(5) William Chaffer, 1899. "Gilda Aurifabrorum - A history of English goldsmiths and plateworkers and their marks stamped on plates", Reeves and Turner, London.
(6) Montague Howard, 1903. "Old London silver – its history, its makers and its marks", Charles Scribner’s Sons, New York.
(7) Charles J. Jackson, 1964. English Goldsmiths and their marks - A history of the goldsmiths and plate workers of England, Scotland and Ireland. Second Edition. Dover Publications Inc., New York.
(8) http://www.silvermakersmarks.co.uk/Makers/London-RR-RZ.html#RR

NOTES

NOTE 1- The attribution of a specific mark to a particular maker is sometime speculative. In the case the doubt is between two makers of pair importance - like Richard Rugg and Robert Rew - the question may have only an academic interest.
NOTE 2 - The term smallworker identify a silversmith who produce only items of small size, like flatware, buckles, watch cases, knife handles, jewelry, etc. Sometime they are better identified as a bucklemaker, watchcasemaker or haftmaker, depending on their specialization.
NOTE 3 - The term largeworker identify a silversmith who mainly produce items of big size, like coffee pot, teapot, salver, etc. They can be also identified with the generic term of plateworker.
NOTE 4 - The question is substantial because, a part the personal skill, a workshop of a largeworker greatly differs in the availability of working tools than that of a smallworker.
NOTE 5 - Chaffer was authorized to reproduce the marks and the information reported in the registers only for personal use. The publication of the “Gilda Aurifabrorum” produced a great irritation at the Goldsmiths’ Hall, with the consequence that future researchers (including Sir Charles Jackson) has no o a very restricted access to the Registers.
NOTE 6 - Apart for the date letter A, where hallmarks are randomly struck as in the previous cycle from 1736 to 1755, the sequence of marks struck at the Goldsmiths’ Hall was: date letter, lion passant and leopard head, with a few exceptions where the lion passant and the crowned leopard head appear inverted, and where the date letter (apparently only the letter Q) is sometime struck at the end of the sequence.
NOTE 7 - I assumed that all the RR marks in a bilobed punch found in my research on silver salvers are pellet between, although in some of the pictures of the Figure 6 it is difficult to realize whether or not this assumption is correct. I found an example of the RR mark in a bilobed punch unpelleted struck underneath a castor dating to 1775-1776 (Figure 7), so this mark, observed by Cripps and Jackson seems to be really existing, but it does not seem to has been used on salvers. Furthermore a close inspection of this mark shows that the difference between the pelleted and unpelleted mark are not limited to the pellet itself, but they (that found on salvers and that reported in the works of Cripps and Jackson) also slightly differ for the shape of the R (compare marks in Figure 6 and 7).
NOTE 8 - Although in some example (especially in one dating 1773) a trace of a pellet between the two big R can be seen, a closed inspection seems to exclude that any of the found marks can be RR pellet between.
NOTE 9 – The register of Large Plate Workers from 1758 to 1773 is missing and then it is likely that some marks may not have been included in the works of Chaffer and Grimwade.
NOTE 10 - The date letter changed on May each year, usually in occasion of the Goldsmiths' Patron day (St. Dunstan, May 19), when the wardens were elected by the Goldsmith’s Company. So, each date letter usually refers to 12 months straddling two years.
 

R•R mark (pellet between, small dimension)	Year
	1754
	1755
	1756
	1756
	1756
	1756
	1757
	1758
	1758
	1759
	1760
	1761
	1762
	1762
	1762
	1762
	1763
	1763
	1763
	1763
	1764
	1764
	1765
	1765
	1765
	1765
	1765
	1765
	1766
	1766
	1766
	1767
	1767
	1768
	1768
	1768
	1769
RR mark (unpelleted, bigger dimension)
	1770
	1770
	1770
	1770
	1771
	1771
	1771
	1771
	1772
	1773
	1773
	1773
	1773
	1773
	1774
	1774
	1774
Richard Rugg R•R mark (pellet between in bilobed punch)
	1774
	1774
	1775 (*)
	1776
	1776
	1779
	1779
	1780
	1781
	1782
	1783

(*) Mark found underneath a snuffer tray (note that the letter R seems to be bigger than that of the other examples) Figure 6 – "RR" marks found during my research on-line and ranked by date letter

Figure 7 - Example of a RR unpelleted mark in a bilobed punch struck underneath a silver castor dating 1775-1776